Answer:
x+3
Step-by-step explanation:
Area of a rectangle is [tex]L\cdot W[/tex].
We know the width, W, is [tex]x-3[/tex] and we know the area is [tex]x^2-9[/tex].
Inputting this in our formula above we get:
[tex]x^2-9=L(x-3)[/tex]
L is a an expression such that when you multiply it to [tex](x-3)[/tex] gives you [tex](x^2-9)[/tex].
[tex]x^2-9[/tex] is a difference of squares and can be factored using:
[tex]a^2-b^2=(a-b)(a+b)[/tex].
[tex]x^2-9=(x-3)(x+3)[/tex].
So L=x-3 and W=x+3.
