Question

If the 12 th term of an ap is -13 and the sum of the first four term is 24 what is the sum of first 10 terms

Answer 1

Answer:

Given :-

T(12) = a+11d = (-13) [ an = a +(n-1)d]

&

S(4) = 2(2a+3d) = 24

a+11d = -13 --------(1)

2a+3d = 12 ---------(2)

multiplying eqn (1) by 2 , subtracting from eqn (2) we get,

2a+3d = 12

2a+22d=-26

-19d = 38

d = -2 ..

putting in eqn now we get, a = 9

so,

sum of 10 terms will be =

s(10) = 10/2(2*9+9(-2))

= 5(18-18)

= 0 (Ans)

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