Question

If 1+4+7+10+...........+x=287, find the value of x

Answer 1

Answer:

265

Step-by-step explanation:1+4+7+10=22

so

22+x=287

x=287-22

which is 265

Answer 2

Answer:

X=40

Step-by-step explanation:

as the given series is in A.P

a=1 , d = 3

sum of terms = n/2(2a+(n-1)d)

287 =n/2(2×1+(n-1)3)

574=n(2+3n-3)

574 = -n+3n^2

3n^2-n-574=0

n = 14

so number of terms is 14

we know that last term is X . so, X is the 14th term

a+13d = 14th term

1+13*3=X

1+39=X

X =40

Hope this answer helps you