Answer:
161
Step-by-step explanation:
We have to calculate the sum of the following:
∑(-2+5n) for n=2 to n=8
Now, the sum =(-2+5×2) + (-2+5×3)+ ..... + (-2+5×8)
=(-2)7 + 5 (2+ 3+ 4+ ....+8) {Since there are 7 terms in the sum}
= -14+ 5 (1+ 2+ 3+ 4+ ....+8 -1)
= -14 + 5{[tex]\frac{8(8+1)}{2} -1[/tex]}
= -14 + 5( 36- 1) {Since the sum of first n natural numbers is [tex]\frac{n(n+1)}{2}[/tex]}
= -14 + 5×35
=161 (Answer)
