Question

in an AP the sum of first n terms is 3n Square by 2 + 13 by 2 find the 25th term

Answer 1

sₓ = 3x²/2 + 13/2
a₂₅ = s₂₅ - s₂₄
 = 3×25²/2 + 13/2 - (3×24²/2 + 13/2)
 = 3×49/2 = 73.5

Answer 2

Sn= 3n^2\2+13\2
=3n^2+13whole ÷by2
S25=3(25)^2+13 whole ÷by2
=3(625)\2+13\2
=1875\2+13\2
=1888\2=844