ข้อ 4 (x+2)(x-6)(x-4)(x+3)=10x^2
( x^2-4x-12)(x^2-x-12)=10x^12
ให้ x^2-12=m --------------->
(m-4x)(m-x)=10x^2
m^2 -5mx+4x^2 =10x^2
m^2 -5mx -6x^2=0 -------------> (m+x)(m-6x)=0
ดังนั้น ( x^2+x-12)(x^2-6x-12)=0
x^2-6x=12 -------> x^2-6x+1=13
__________________
ok
|