Question

Solve the summation from n equals 2 to 8 of negative 2 plus 5 times n. 92 146 161 164

plz hurrrrry

Answer 1

161

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{
`(8(8+1))/(2) -1`}

= -14 + 5( 36- 1) {Since the sum of first n natural numbers is
`(n(n+1))/(2)`}

= -14 + 5×35

=161 (Answer)