Question

in an ap the the sum of first ten terms is -150 and sum of next ten terms is -550 find ap

Answer 1

S10=10/2(2a+9d)

-150=5(2a+9d)

-150=10a+45d___(1)

S20-S10=20/2[2a+19d]-10/2[2a+9d]

-550=10(2a+19d)-5(2a+9d)

-550=20a+190d-10a-45d

-550=10a+145d___(2)

(2)-(1)==>100d=-400

==>d=-4

put d=-4 in (1)

-150=10a+45*-4

-150=10a-180

10a=180-150

10a=30

a=3

A.P===>3,-1,-5,-9