Question

if the sum of first nth term of AP is 4x- x square what is the sum of first 2 term what is the second term find the third the tenth and the nth whole solution

Answer 1

Step-by-step explanation:

Sn= -x²+4x

d= 2× coefficient of x²

d= 2×(-1)= -2

S2=4x-x²=4×2-2²=8-4= 4

a2=a+(n-1)d

d= -2

now for any A.P ,S1=a1=4×1-1²= 3

a=3

a2=a+(2-1)d= 3+(-2)= 1

a2=1

a3=a+2d=3+2×(-2)=3-4= -1

a10 =a+9d = 3+9×-2=3-18= -15

an= a+(n-1)d= 3-2(n-1) = 5-2n