Question

a1 ,a2, a3,..........an forms AP.
an = 3+4n
find the sum of first 15 terms in each case​

Answer 1

$\huge\boxed{\fcolorbox{white}{magenta}{Answer}}$

$\Large\boxed{an=3+4n}$

for the AP

n = 1,

a1 = 3 + 4 × 1 = 7

a2 = 3 + 4 × 2 = 11

a3 = 3 + 4 × 3 = 15

.

.

.

a15 = 3 + 4 × 15 = 63

therefore AP will be

7 , 11 , 15 , ..................63

for the sum of the given AP

$\Large\boxed{sn=n/2(a+l)}$

S15 = 15/2 × { 7 + 63 }

S15 = 15/2 × 70

S15= 15 × 35

$\Large\boxed{S15=525}$

I hope it will helps u...☺️