Please solve the following problem by using factoring and the zero-product property.

Question

9r^2-30r+21=-4

Thanks

Answer 1

9r^2-30r+21 = -4
9r^2-30r+25 = 0

Note that 9 and 25 are perfect squares, so a good thing to try is

(3r-5)^2 = 0

Yep, that's it.

So, there is a double root of x = 5/3