Question

Find the value of x if the sum of n terms is given 1+4+7+.....+x=287

Answer 1

$\frac{1 + 4 + 7 + x}{4} = 287$
$12 + x = 287 \times 4 \\ = 1568$
$x = 1568 - 12 = 1556$

$x = 1556$
I hope this is correct....