Let Sn denote the sum of the first n terms of an A.P.

Question

Let Sn denote the sum of the first n terms of an A.P. If S4 = 16 and S6= -- 48, then S10 is equal to :

Accepted Answer

S4 = $${4 \over 2}\left( {2a + 3d} \right) = 16$$

$$ \Rightarrow 2a + 3d = 8$$

S4 = $${6 \over 2}\left( {2a + 5d} \right) = -48$$

$$ \Rightarrow 2a + 5d = -16$$

$$ \therefore $$ d = -12 and a = 22, Now S10 = $${{10} \over 2}\left( {44 - 108} \right) =  - 320$$

Solutions · 1