Question

how many term of AP 11 ,-9,-7...... must be take to give a sum of -357 explain the reason of double ans

Answer 1

hey mate here your answer **

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sn =-357

a=11
d=-9-11 =-20

sn= n/2(2a+(n-1)d
-357=n/2 (2×11+(n-1)-20
-714 =n(22+(n-1)-20
-714=n(22-20n+20)
-714= n (42-20n)
-714 = 42n -20n2

-20n2+42n =-714

you solve this eqn and then find 2 factor