NCERT Solutions for Class 7 Maths Chapter 7 Congruence of Triangles
NCERT solutions for class 7 maths chapter 7 congruence of triangles topic 7.5
1. When two triangles, say ABC and PQR are given, there are, in all, six possible matchings or correspondences. Two of them are:
and
Find the other four correspondences by using two cutouts of triangles. Will all these correspondences lead to congruence? Think about it.
Answer:
the other four correspondences by using two cutouts of triangles are :
NCERT solutions for class 7 chapter 7 congruence of triangles topic 7.6
1. In Fig 7.14, lengths of the sides of the triangles are indicated. By applying the SSS congruence rule, state which pairs of triangles are congruent. In case of congruent triangles, write the result in symbolic form:
Answer:
i) Since
AB = PQ
BC = QR
CA = PR
So, by SSS congruency rule both triangles are congruent to each other.
ii) Since,
ED = MN
DF = NL
FE = LM
So, by SSS congruency rule both triangles are congruent to each other.
.
iii) Since
AC = PR
BC = QR But
So the given triangles are not congruent.
iv) Since,
AD = AD
AB = AC
BD = CD
So, By SSS Congruency rule, they both are congruent to each other.
.
2. In Fig 7.15, and D is the mid-point of .
(i) State the three pairs of equal parts in and
(ii) Is Give reasons.
(iii) Is Why?
Answer:
Here in and
i) Three pair of equal parts are:
AD = AD ( common side )
BD = CD ( as d is the mid point of BC)
AB = AC (given in the question)
ii) Now,
by SSS Congruency rule,
iii) As both triangles are congruent to each other we can compare them and say
.
3. In Fig 7.16, and . Which of the following statements is meaningfully written?
Answer:
Given,
and
.
AB = AB ( common side )
So By SSS congruency rule,
.
So this statement is meaningfully written as all given criterions are satisfied in this.
1. ABC is an isosceles triangle with (Fig 7.17). Take a trace-copy of and also name it as
(i) State the three pairs of equal parts in .
(ii) Is ? Why or why not?
(iii) Is ? Why or why not?
Answer:
Here, in .
i)the three pairs of equal parts in are
AB = AC
BC = CB
AC = AB
ii)
Hence By SSS Congruency rule, they both are congruent.
iii) Yes, because are congruent and by equating the corresponding parts of the triangles we get,
.
1. Which angle is included between the sides and of ?
Answer:
Since both the sides and intersects at E,
is included between the sides and of .
2. By applying SAS congruence rule, you want to establish that . It is given that and . What additional information is needed to establish the congruence?
Answer:
To prove congruency by SAS rule, we need to equate two corresponding sides and one corresponding angle,
so in proving we need,
And
.
Hence the extra information we need is .
3. In Fig 7.24, measures of some parts of the triangles are indicated. By applying SAS congruence rule, state the pairs of congruent triangles, if any, in each case. In case of congruent triangles, write them in symbolic form.
Answer:
i) in and
AB = DE
AC = DF
Hence, they are not congruent.
ii) In and
AC = RP = 2.5 cm
CB = PQ = 3 cm
Hence by SAS congruency rule, they are congruent.
.
iii) In and
DF= PQ = 3.5 cm
FE= QR = 3 cm
Hence, by SAS congruency rule, they are congruent.
iv) In and
QP = SR = 3.5 cm
PR = RP (Common side)
Hence, by SAS congruency rule, they are congruent.
.
1. What is the side included between the angles and N of ?
Answer:
The side MN is the side which is included between the angles and N of .
2. You want to establish , using the ASA congruence rule. You are given that and . What information is needed to establish the congruence? (Draw a rough figure and then try!)
Answer:
As we know, in ASA congruency two angles and one side is equated to their corresponding parts. So
To Prove
And The side joining these angles is
.
So the information that is needed in order to prove congruency is .
4. In Fig 7.25, and bisect each other at .
(i) State the three pairs of equal parts in two triangles and .
(ii) Which of the following statements are true?
Answer:
i) The three pairs of equal parts in two triangles and are:
CO = DO (given)
OA = OB (given )
( As opposite angles are equal when two lines intersect.)
ii) So by SAS congruency rule,
that is
Hence, option B is correct.
3. In Fig 7.27, measures of some parts are indicated. By applying ASA congruence rule, state which pairs triangles are congruent. In case of congruence, write the result in symoblic form.
Answer:
i) in and
AB = FE = 3.5 cm
So by ASA congruency rule, both triangles are congruent.i.e.
ii) in and
But,
So, given triangles are not congruent.
iii) in and
RQ = LN = 6 cm
So by ASA congruency rule, both triangles are congruent.i.e.
.
iv) in and
AB = BA (common side)
So by ASA congruency rule, both triangles are congruent.i.e.
4. Given below are measurements of some parts of two triangles. Examine whether the two triangles are congruent or not, by ASA congruence rule. In the case of congruence, write it in symbolic form.
Answer:
i)
Given in and .
So, by ASA congruency criterion, they are congruent to each other.i.e.
.
ii)
Given in and .
For congruency by ASA criterion, we need to be sure of equity of the side which is joining the two angles which are equal to their corresponding parts. Here the side QR is not given which is why we cannot conclude the congruency of both the triangles.
iii)
Given in and .
For congruency by ASA criterion, we need to be sure of equity of the side which is joining the two angles which are equal to their corresponding parts. Here the side QR is not given which is why we cannot conclude the congruency of both the triangles.
5. In Fig 7.28, ray AZ bisects as well as .
(i) State the three pairs of equal parts in triangles and .
(ii) Is Give reasons.
(iii) Is Justify your answer.
(iv) Is Give reasons.
Answer:
i)
Given in triangles and
( common side)
ii)
So, By ASA congruency criterion,triangles and <img alt="DAC" height="12"
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iii)
Since , all corresponding parts will be equal. So
.
iv)
Since , all corresponding parts will be equal. So
NCERT solutions for class 7 maths chapter 7 congruence of triangles topic 7.7
1. In Fig 7.32, measures of some parts of triangles are given.By applying RHS congruence rule, state which pairs of triangles are congruent. In case of congruent triangles, write the result in symbolic form.
Answer:
i) In and
Hence they are not congruent.
ii)
In and
( same side )
So, by RHS congruency rule,
iii)
In and
( same side )
So, by RHS congruency rule,
iv)
In and
( same side )
So, by RHS congruency rule,
2. It is to be established by RHS congruence rule that . What additional information is needed, if it is given that
and
Answer:
To prove congruency by RHS (Right angle, Hypotenuse, Side ) rule, we need hypotenuse and side equal to the corresponding hypotenuse and side of different angle.
So Given
( Right angle )
( Side )
So the third information we need is the equality of Hypotenuse of both triangles. i.e.
Hence, if this information is given then we can say,
.
3. In Fig 7.33, and are altitudes of such that .
(i) State the three pairs of equal parts in and .
(ii) Is ? Why or why not?
(iii) Is ? Why or why not?
Answer:
i) Given, in and .
ii) So, By RHS Rule of congruency, we conclude:
iii) Since both the triangle are congruent, all parts of one triangle are equal to their corresponding part from another triangle.
So.
.
4. ABC is an isosceles triangle with and is one of its altitudes (Fig 7.34).
(i) State the three pairs of equal parts in and .
(ii) Is ? Why or why not?
(iii) Is ? Why or why not?
(iv) Is ? Why or why not?
Answer:
i) Given in and .
( Common side)
ii) So, by RHS Rule of congruency, we conclude
iii) Since both triangles are congruent all the corresponding parts will be equal.
So,
iv) Since both triangles are congruent all the corresponding parts will be equal.
So,
.
NCERT solutions for class 7 maths chapter 7 congruence of triangles exercise 7.1
1. Complete the following statements:
(a) Two line segments are congruent if ___________.
(b) Among two congruent angles, one has a measure of ; the measure of the other angle is ___________.
(c) When we write , we actually mean ___________.
Answer:
a) Two line segments are congruent if they are identical in shape and size and which is the case when the length of two line segments are equal.
b) As the congruent things are a photocopy of each other.
c) When we write , We mean that both the angles(A & B) are equal.
2. Give any two real-life examples for congruent shapes.
Answer:
Any two things that have identical shape and size are congruent like all the same kind of pens are congruent to one another. every same kind of bench in class are congruent to one another.all the similar football is congruent to one another.
3. If under the correspondence write all the corresponding congruent parts of the triangles.
Answer:
Corresponding parts of the two congruent triangles are :
Sides:
Angles:
4. If write the part(s) of that correspond to
Answer:
Given,
The part of that correspond to
NCERT solutions for class 7 maths chapter 7 congruence of triangles exercise 7.2
1.(a) Which congruence criterion do you use in the following?
Answer:
Since we are comparing all the sides of two triangles, The SSS (side, side, side) Congruent criterion is used.
1.(b) Which congruence criterion do you use in the following?
Answer:
Since we are comparing two sides and one angle of the two triangles, the SAS (sie, angle, side) congruent criterion is used to prove them congruent.
1.(c) Which congruence criterion do you use in the following?
Answer:
Since we are comparing two angles and one side, ASA(Angle, Side, Angle) congruency criterion is used to prove the congruency.
1.(d) Which congruence criterion do you use in the following?
Answer:
Since we are comparing two sides and one angle of the two triangles, the SSA (Side, Side, Angle) congruent criterion is used to prove the congruency.
2.(a) You want to show that
(a) If you have to use criterion, then you need to show
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Answer:
As we know that in the criterion of proving congruent, all three corresponding sides are equal to another. So to prove the congruency, we kneed to know the following things:
2.(b) You want to show that
(b) If it is given that and you are to use SAS criterion, you need to have
Answer:
As we know in SAS criterion the two sides and one angle are identical to their corresponding parts of another triangle. So to prove congruency we need to prove that,
2.(c) You want to show that
(c) If it is given that and you are to use ASA criterion, you need to have
Answer:
Given,
also,
Now, As we know in the ASA criterion of proving congruency, the one and side two angles are equal to their corresponding parts. So,
3. You have to show that . In the following proof, supply the missing reasons.
Steps |
Reasons |
Answer
Steps |
Reasons |
Given in the question |
|
Given in the question. |
|
the side which is common in both triangle |
|
By SAS Congruence Rule |
4. In , , and .
In , , and . A student says that by AAA congruence criterion. Is he justified? Why or why not?
Answer:
No, because it is not necessary that two triangles will be congruent if their all three corresponding angles are equal. in this case, the triangles might be zoomed copy of one another.
5. In the figure, the two triangles are congruent. The corresponding parts are marked. We can write ?
Answer:
Comparing from the figure.
By SAS Congruency criterion, we can say that
]
6. Complete the congruence statement:
Answer:
Comparing from the figure, we get,
So By SSS Congruency Rule,
Also,
Comparing from the figure, we get,
So By SSS Congruency Rule,
.
7. In a squared sheet, draw two triangles of equal areas such that
(i) the triangles are congruent.
(ii) the triangles are not congruent.
What can you say about their perimeters?
Answer:
When two triangles are congruent, the corresponding parts are exactly identical so they have the same area and perimeter.
While the triangles are not congruent but have the same area, then the perimeter of both triangles are not equal.
8. Draw a rough sketch of two triangles such that they have five pairs of congruent parts but still the triangles are not congruent.
Answer:
Five pairs of congruent parts can be three pairs of sides and two pairs of angles. In that case, the SAS or ASA criterion would prove them to be congruent. Hence, such a figure is not possible.
9. If and are to be congruent, name one additional pair of corresponding parts. What criterion did you use?
Answer:
Given
One additional pair which is not given in the figure is
We used the ASA Criterion as the two corresponding angles are given and we figured out the side by congruency.
10. Explain, why
Answer:
Comparing both triangles, we have,
So By RHS congruency criterion,
.
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