Đáp án:
Giải thích các bước giải:
Bai1:
$a)x^2-y^2-5x+5y_{}$
$=(x^2-y^2)-(5x-5y)_{}$
$=(x-y)(x+y)-5(x-y)_{}$
$=(x-y)(x+y-5)_{}$
$b)3(x-y)-5x (y-x)_{}$
$=3(x-y)+5x(x-y)_{}$
$=(x-y)(3+5x)_{}$
$c) x^3+12x^2+48x+64=x^3+3.x^2.4+3.x.4^2+4^3=(x+4)^3_{}$
Bài 2 :
$a)127^2+146.127+73^2=127^2+2.73.127+73^2=(127+73)^2=200^2=40000_{}$
$b)5x(x-4y)-4y(y-5x)=5x^2-20xy-4y^2+20xy=5x^2-4y^2_{}$
Tại $x=_{}$$\frac{-1}{5}$ ; $y=_{}$$\frac{-1}{2}$ ta có :;
$5_{}$($\frac{-1}{5}$) $^{2}$ - $4_{}$($\frac{-1}{2}$) $^{2}$
$=5._{}$ $\frac{1}{25}$ $-4._{}$$\frac{1}{4}$ $= _{}$$\frac{1}{5}$ $-_{}$$1 = $ $\frac{-4}{5}$
