solve x2−7x=0 by factoring.

x^2 - 7x = 0
Factoring:-
x(x - 7) = 0
x = 0'  x  - 7 = 0 so x = 7

Solution is 0, 7.

First just break it down,
set the value of x to 0 for the equation.
So already x=0.  
x(7+x)=0
-7+x=0
-7+7=0 
Your answer is
x=0
x=7