Question

Simplify x²-49/3x+21

Answer 1

$x^2-49=x^2-7^2=(x-7)(x+7)\\\\\text{Used}\ a^2-b^2=(a-b)(a+b)\\\\3x+21=3\cdot x+3\cdot7=3(x+7)\\\\\dfrac{x^2-49}{3x+21}=\dfrac{(x-7)(x+7)}{3(x+7)}=\dfrac{x-7}{3}$

Answer 2

First, you factor and simplify (respectively) the numerator and denominator. Your equation becomes:

$\frac{(x-7)(x+7)}{3(x + 7)}$

Notice, there is a (x + 7) on both the top and the bottom. Because of this, they cancel each other out. What is left is your answer:

$\frac{(x-7)}{3}$