assuming
[tex] \sqrt{3x+12} =x[/tex]
sqare both sides
3x+12=x²
minus 3x+12 both sides
x²-3x-12=0
factor
we can't
use quadratic formula
for
ax²+bx+c=0
[tex]x= \frac{-b+/- \sqrt{b^2-4ac} }{2a} [/tex]
so
[tex]x= \frac{-(-3)+/- \sqrt{(-3)^2-4(1)(-12)} }{2(1)} [/tex]
simplfying we get
[tex]x= \frac{3+ \sqrt{57} }{2} [/tex] or [tex]x= \frac{3- \sqrt{57} }{2} [/tex]
