Question

solve by completing the square: 3x^2-9x-12=0

Answer 1

\[3x^2-9x-12=0\] divide by 3 get
\[x^2-3x-4=0\] add 4 get
\[x^2-3x=4\] take half of three get
\[(x-\frac{3}{2})^2=4+\frac{9}{4}=\frac{25}{4}\]
then take the square root of both sides get
\[x-\frac{3}{2}=\pm\frac{5}{2}\] and finally
\[x=\frac{3}{2}+\frac{5}{2}=\frac{8}{2}=4\] pr
\[x=\frac{3}{2}-\frac{5}{2}=\frac{-2}{2}=-1\]

Answer 2

it would have been tonnes easier to factor as
\[(x+1)(x-4)=0\] etc

Answer 3

youre the best!!

Answer 4

ty (blush)