Question

In an AP the sum of first 10 terms is -80 and sum of next 10 terms is -280 find the AP.

Answer 1

Answer:

Given,

S

10

=−150

S

20

−S

10

= Next 10 term

S

20

−S

10

=−550

S

20

=−550+S

10

S

20

=−550−150

S

20

=−700

S

n

=

2

n

[2a+(n−1)d]

S

10

=

2

10

[2a+(10−1)d]=−150

2a+9d=−30 (i)

S

20

=−700

2

20

[2a+19d]=−700

2a+19d=−70 (ii)

eq(i)-eq(ii)

(2a+9d=−30)−(2a+19d=−70)

−10d=40

d=−4

2a+9d=−30

2a=−30+36

⇒a=3

So the A.P. will be as:-

a, (a+d), (a+2d), ...

3, (-1), (-5) & so on

Mark as Brainleist Answer

Answer 2

Answer:

In an AP the sum of first 10 terms is -80 and sum of next 10 terms is -280 find the AP.