Phân tích đa thức thành nhân tử:
a, x^3-4x^2-8x+8
b,x^2+2x-15
c,(x+2)(x+3)(x+4)(x+5)-24
Phân tích đa thức thành nhân tử: a, x^3-4x^2-8x+8 b,x^2+2x-15 c,(x+2)(x+3)(x+4)(x+5)-24
By Ruby
By Ruby
Phân tích đa thức thành nhân tử:
a, x^3-4x^2-8x+8
b,x^2+2x-15
c,(x+2)(x+3)(x+4)(x+5)-24
a)x³-4x²-8x+8=(x³+2x²)-(6x²+12x)+(4x+8)
=x²(x+2)-6x(x+2)+4(x+2)=(x²-6x+4)(x+2)
b)x²+2x-15=(x²-3x)+(5x-15)=x(x-3)+5(x-3)=(x+5)(x-3)
c)A=(x+2)(x+3)(x+4)(x+5)-24=(x+2)(x+5)(x+3)(x+4)-24
=(x²+7x+10)(x²+7x+12)-24
Đặt x²+7x+10=a⇒A=a(a+2)-24=a²+2a-24=(a²-4a)+(6a-24)=(a+6)(a-4)
⇒A=(x²+10x+16)(x²+10x+6)
$a)x³-4x²-8x+8$
$=(x³+2x²)-(6x²+12x)+(4x+8)$
$=x²(x+2)-6x(x+2)+4(x+2)$
$=(x²-6x+4)(x+2)$
$b)x²+2x-15$
$=(x²-3x)+(5x-15)$
$=x(x-3)+5(x-3)$
$=(x+5)(x-3)$
$ c)A=(x+2)(x+3)(x+4)(x+5)-24$
$=(x+2)(x+5)(x+3)(x+4)-24$
$=(x²+7x+10)(x²+7x+12)-24$
$Đặt x²+7x+10=a$ $A=a²+2a-24$
$=(a²-4a)+(6a-24)$
$=(a+6)(a-4)$
$⇒A=(x²+10x+16)(x²+10x+6)$