Đáp án+Giải thích các bước giải:
Câu 1:
$a) x(x-y)+y(x-y)$
$=x²-xy+xy-y²$
$=x²-y²$
$b) (x²-2xy+y²)(x-y)-(x-y)(x²+xy+y²)$
$=(x-y)(x²-2xy+y²-x²-xy-y²)$
$=(x-y)(2xy-y)$
$=2x²y-xy-2xy²+y²$
$c) 7x(4y-x)+4y(y-7x)-(4y²-7x)$
$=7x(−x+4y)+4y(−7x+y)−(4y²−7x)$
$=7x²+28xy−28xy+4y²−4y²+7x$
$=−7x²+7x$
$d) (2x+y)(2z+y)+(x-y)(y-z)$
$=(2x+y)(y+2z)+(x-y)(y-z)$
$=2xy+4xz+y²+2yz+xy−xz−y²+yz$
$=3xy+4xz+3yz−xz$
Câu 2:
$a) 3x(12x-4)-9x(4x-3)=30$
$⇔36x²-12x-(36x-27x)=30$
$⇔36x²-12x-36x+27x=30$
$⇔15x=30$
$⇔x=2$
$b) 4x(7x-5)-7x(4x-2)=-12$
$⇔28x²−20x−28x²+14x=−12$
$⇔−6x=−12$
$⇔x=2$
$c) 3x(2x-4)-(6x-1)(x+2)=25$
$⇔6x²−12x−(6x²+12x−x−2)=25$
$⇔6x²−12x−(6x²+11x−2)=25$
$⇔6x²−12x−6x²−11x+2=25$
$⇔−23x+2=25$
$⇔-23x=25-2$
$⇔-23x=23$
$⇔-1$
Chúc bn hc tốt🥰
`\text{#LinhSad}`
