Question

Write the sum in sigma notation 72 + 61 + 50 + 39 +...+ -104 ??

`sum_(k=1)^AB`

I'm given; "The answer for A should be a number and the answer for B should be an expression."

Answer 1

Shown below

Explanation:

Here the `k^"th"` term is `-11k + 83`

So the first term, at `k=1` is 72 and the final term is -104

Hence `-11k + 83 = -104 => k = 17`

Hence we are summing up from `k=1` to `k = 17` of `-11k + 83`

Hence `sum_(k=1) ^17 (-11k +83)`