Question

If sum of first 6 terms of an A.P is 36 and that of the first 16 terms is 256.Find the sum of first 10 terms.​

Answer 1

Answer:

100 term

Step-by-step explanation:

We have the sum of first n terms of an AP,

S

n

=

2

n

[2a+(n−1)d]

Given,

36=

2

6

[2a+(6−1)d]

12=2a+5d ---------(1)

256=

2

16

[2a+(16−1)d]

32=2a+15d ---------(2)

Subtracting, (1) from (2)

32−12=2a+15d−(2a+5d)

20=10d ⟹d=2

Substituting for d in (1),

12=2a+5(2)=2(a+5)

6=a+5 ⟹a=1

∴ The sum of first 10 terms of an AP,

S

10

=

2

10

[2(1)+(10−1)2]

S

10

=5[2+18]

S

10

=100

This is the sum of the first 10 terms

Answer 2

Answer:

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