Question

If an = 3n-5, find s10​

Answer 1

Answer:

Hey mate please refer to the attachment for the answer.

Answer 2

$\huge\mathbb{GIVEN}$

an = 3n -5

$\huge\mathbb{SOLUTION}$

putting n = 1

a1 = 3×1 -5

a1 = 3-5

a1 = -2

putting n = 2

a2 = 3×2-5

a2 = 6-5

a2 = 1

so,

First term = -2

common difference =a2-a1= 1-(-2) = 1+2= 3

S10 = n/2 (2a+(n-1)×d)

S10 = 10/2(2×(-1)+(10-1)×3)

S10 =5(-2+27)

S10 =5×25

S10 = 125