Question

Can you help me find the indicated sum? Thanks!

Answer 1

`sum_(k=1)^(k=4)(-1)^k(k+11)=2`

Explanation:

.

`k=1 :. a_1=(-1)^1(1+11)=-12`

`k=2 :. a_2=(-1)^2(2+11)=13`

`k=3 :. a_3=(-1)^3(3+11)=-14`

`k=4 :. a_4=(-1)^4(4+11)=15`

`sum_(k=1)^(k=4)(-1)^k(k+11)=-12+13-14+15=28-26=2`