Let the four numbers be
(
a
−
3
d
)
,
(
a
−
d
)
,
(
a
+
d
)
and
(
a
+
3
d
)
.
Given:
1. Their sum is
28
(
a
−
3
d
)
+
(
a
−
d
)
+
(
a
+
d
)
+
(
a
+
3
d
)
=
28
⇒
4
a
=
28
∴
a
=
7
.
2.Their sum of square
216
(
a
−
3
d
)
2
+
(
a
−
d
)
2
+
(
a
+
d
)
2
+
(
a
+
3
d
)
2
=
216
⇒
a
2
+
9
d
2
−
6
a
d
+
a
2
+
d
2
−
2
a
d
+
a
2
+
d
2
+
2
a
d
+
a
2
+
9
d
2
+
6
a
d
=
216
⇒
4
a
2
+
20
d
2
=
216
⇒
a
2
+
5
d
2
=
54
Putting the value of
a
49
+
5
d
2
=
54
5
d
2
=
5
d
2
=
1
∴
d
=
±
1
.
For
d
=
1
:
The numbers are
7
+
3
,
7
+
1
,
7
−
1
,
7
−
3
⇒
10
,
8
,
6
,
4
.
For
d
=
−
1
:
The numbers are
7
+
3
,
7
+
1
,
7
−
1
,
7
+
3
⇒
4
,
6
,
8
,
10
.
Q.
Divide 32 into four parts which are the four terms of an AP such that the product of the first and the fourth terms is to the product of the second and the third terms as 7:15.
Solution:
In case of 4 terms, we usually take 2d as the common difference and the average of the two middle terms should be a.
Therefore, Let a-3d, a-d, a+d and a+3d be the 4 terms.
Now, By Question, we have
(a-3d) + (a-d) + (a+d) + (a+3d) = 32
=> 4a = 32
=> a = 8
Again, By Question, we have
(a-3d) (a+3d) : (a-d) (a+d) = 7 : 15
=>
a
2
−
9
d
2
:
a
2
−
d
2
= 7 : 15
=>
15
(
a
2
−
9
d
2
)
=
7
(
a
2
−
d
2
)
=>
15
a
2
−
135
d
2
.
=
7
a
2
−
7
d
2
=>
15
a
2
−
7
a
2
.
=
135
d
2
−
7
d
2
=>
8
a
2
.
=
128
d
2
=>
8
(
8
)
2
.
=
128
d
2
(Substituting the value of a)
=>
512.
=
128
d
2
=>
4.
=
d
2
=>
d
=
+
2
,
−
2
Therefore Common Difference = 2d = (+)(-)4
Therefore, The required AP is -
a-3d = 8 - 3(2) = 2. Or. a-3d = 8-3(-2) = 14
a-d. = 8 - 2. = 6. Or. a-d. = 8-(-2) = 10
a+d. = 8+2. = 10. Or. a+d. = 8+(-2) = 6
a+3d = 8+3(2) = 14. Or. a+3d = 8+3(-2) = 2
Note: In one case the Common Difference is 4 where as in the 2nd case the Common Difference is -4.
Q.
The sum of first three terms of an AP is 48. If the product of first and second terms exceeds 4 times the third term by 12. find the AP.
Solution:
let the first 3 terms of the A.P be a-d, a and a+d
by data, (a-d) + a + (a+d)= 48
3a=48
a=16
as per data: (a-d)a= 4(a+d)+12--(1)
substituting the value of 'a' in (1); (16-d)16=4(16+d) +12
256 - 16d = 64 + 4d + 12
256 - 16d =76 + 4d
256-76= 16d+4d
180 = 20d
d= 9
therefore the A.P is : 16, 25, 34...
Benefits of RS Aggarwal Solutions for Class 10 Maths Chapter 11 Exercise 11.2
-
Clear Explanations:
Provides easy-to-understand explanations of Arithmetic Progressions (AP) concepts.
-
Step-by-Step Guidance:
Guides students through solving problems with detailed step-by-step solutions.
-
Enhanced Understanding:
Helps students grasp how to find specific terms in AP sequences.
-
Improved Problem-Solving Skills:
Enhances students ability to solve AP-related problems confidently.
-
Exam Preparation:
Prepares students effectively for exams by covering essential AP topics.
-
Boosts Confidence:
Builds confidence in tackling AP questions in tests and assessments.
-
Comprehensive Coverage:
Covers all aspects of Chapter 11 Exercise 11.2, ensuring thorough understanding.
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