# Math Help - a consecutive number question

1. ## a consecutive number question

$

11+13+15..........+(2n-1)=n^2 - x^2
$

x=?

A) 3
B) 4
C) 5
D) 6
E) 7

2. Originally Posted by OPETH
$

11+13+15..........+(2n-1)=n^2 - x^2
$

x=?

A) 3
B) 4
C) 5
D) 6
E) 7
Can you find the value of the left hand side by using the formula for the sum of an arithmetic series ......? a = 11, d = 2, number of terms = n - 5.

Then equate the value of the left hand side to n^2 - x^2 and solve for x.