substitute the polynomials

Question

(-5r^2+5r+4)-(7r^2+4)

Answer 1

Substitute or subtract?

I'm guessing you mean subtract

essentially you are just subtracting the like terms

-5r^2 subtract 7r^2 is  -12r^2

5r subtract nothing because there is not an r to the first power in the second polynomial.

4 subtract 4 is 0

Put it all together and you get

-12r^2+5r

It might be more proper to list the positive term first

5r - 12r^2

either way would be correct.