Question

Find the sum of 17 term of an ap whose 4 term and 9 term are –15 and –30

Answer 1

Answer:

4th term=a+3d=(-15)

a=(-15)-3d

9th term=a+8d=(-30)

-15-3d+8d=(-30)

5d=(-15)

d=(-3)

a=(-15)-3(-3)=(-5)

Sum=17/2{2×(-5)+(17-1)+(-3)}

=17(-5-24)

=17(-29)=(-493)

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