Question

If f(x) = 8x2 - 18x + 5, find when f(x) = -4

Answer 1

Setting the given equation equals -4 we get:

`\begin{gathered} 8x^2-18x+5=-4 \\ 8x^2-18x+5+4=0 \\ 8x^2-18x+9=0 \end{gathered}`

Notice that:

`8x^2-18x+9=8(x^2-(9)/(4)x+(9)/(8))=8(x-(3)/(2))(x-(3)/(4))`

Therefore, f(x)=-4 when x=3/2 or x=3/4.