Question

find the sum of the AP -10,-8,-6....16term​

Answer 1

hey

a = -10

d = -8+10 = 2

n = 16

sn = n/2{2a+(n-1)d}

s16 = 16/2 {2(-10)+(16-1)2}

= 8 {-20+30}

= 8 {10}

= 80

Answer 2

to find the sum of the AP we need only two terms 1st and 16th.

a= -10, d = 2 n = 16

a16 = a +15d

a16 = -10 + 15*2

a16 = -10 +30

a16 = 20

the formula to find the sum of AP is.

$sn = \frac{n}{2} \times (a + l)$

Sn = 16/2 * (-10 + 20)

Sn = 8*10

Sn = 80

hence the sum of first 16th terms is 80