Question

Deniz tried to subtract two polynomials. Her work is shown below.

Answer 1

Deniz made a mistake in step 2. He tried to use the associative property to group certain terms together, however, to do to that they must have the same variable and exponent. 3r^2 can be combined with 5r^2 but neither of them can be combined with 9r or 7r because those two aren't squared. The correct answer would be:
(3+5)r^2+(-9-7)r+(3+2)
8r^2-16r+5 is your answer

Hope this helped!