Toán Lớp 8: b)x^2-2xy+y^2-9Z^2 c)x^3-3x^2+3x-9 d)x^2-10x+21 làm các bước ra ạ e)2x.(x-3)+5.(3-x)

Question

Toán Lớp 8:  b)x^2-2xy+y^2-9Z^2 c)x^3-3x^2+3x-9 d)x^2-10x+21             làm các bước ra ạ e)2x.(x-3)+5.(3-x)

haiyemy · Answer

$b)x^2-2xy+y^2-9z^2$   $=(x-y)^2-(3z)^2$   $=(x-y+3z)(x-y-3z)$   $c)x^3-3x^2+3x-9$   $=x^2(x-3)+3(x-3)$   $=(x-3)(x^2+3)$   $d)x^2-10x+21$   $=x^2-7x-3x+21$   $=x(x-7)-3(x-7)$   $=(x-7)(x-3)$   $e)2x.(x-3)+5.(3-x)$   $=2x(x-3)-5(x-3)$   $=(x-3)(2x-5)$

thanoanghha · Answer

Lời giải và giải thích chi tiết:    b)x&sup2;-2xy+y&sup2;-9z&sup2;     =(x&sup2;-2xy+y&sup2;)-9z&sup2;     =(x-y)&sup2;-9z&sup2;     =(x-y-3z)(x-y+3z)     c)x&sup3;-3x&sup2;+3x-9     =(x&sup3;-3x&sup2;)+(3x-9)     =x&sup2;(x-3)+3(x-3)     =(x&sup2;+3)(x-3)     d)x&sup2;-10x+21     =x&sup2;-3x-7x+21     =(x&sup2;-3x)-(7x+21)     =x(x-3)-7(x-3)     =(x-7)(x-3)     e)2x.(x-3)+5.(3-x)     =2x.(x-3)-5.(x-3)     =(2x-5)(x-3)     mong đc ctlhn