Question

if 9 th term of ap is zero then find the sum of first 17 terms of Ap​

Answer 1

Answer:

T4=−15=a+(4−1)d

−15=a+(3)d  (1)

T9=−30=a+(9−1)d

−30=a+(8)d  (2)

Where a is the first term of A.P and d is the difference between two terms.

(2)-(1) gives

−15=5d

d=−3 (3)

Substiyutin (3) in (1)

−15=a+3(−3)

−15=a−9

a=−6

S17=2n(2a+(n−1)d)

S17=217(2(−6)+(17−1)d)

S17=217(−12+(16)(−3))

S17=217(−60)

S17=17×−30=−510

Hence the correct answer is −510