-3(x-5y)(x+5y)-4(x+5y) simplify

Question

How to do simplifying the right way

Answer 1

Spot the factor (x+5y) common to both terms and take it outside: (x+5y)(...).

Now we can work out the other brackets: (x+5y)(-3(x-5y)-4). Expand the inner brackets: -3x+15y-4.

So we get (x+5y)(-3x+15y-4) which can be better written: (x+5y)(15y-3x-4). We can expand the whole thing so more terms can be combined: 15xy-3x^2-4x+75y^2-15xy-20y=75y^2-3x^2-4x-20y.

We get the same result if we expand the original:

-3(x^2-25y^2)-4x-20y=-3x^2+75y^2-4x-20y=75y^2-3x^2-4x-20y.