Question

(x+6)(x^2-8x+16)=9(4-x)

Answer 1

$(x+6)(x^2-8x+16)=9(4-x)$
$x^2-8x+16=0 \\ D=64-64=0 \\ x=8/2=4$
$(x+6)(x-4)^2-9(4-x)=0 \\ (4-x)((x+6)(4-x)-9)=0 \\ (4-x)(-x^2-2x+24-9)=0 \\ (4-x)(-x^2+2x+15)=0$