Đáp án+Giải thích các bước giải:
Câu 1: Rút gọn biểu thức:
$a) (2x-3y)²-(4x-y)(y-2)$
$=(2x−3y)(2x−3y)−(4x−y)(y−2)$
$=4x²−6xy−6xy+9y²−(4xy-8x-y²+2y)$
$=4x²−6xy−6xy+9y²−4xy+8x+y²-2y$
$=4x²−16xy+10y²+8x−2y$
$b) (2x+1)(4x²-2x+1)-(x-1)(8x²-1)$
$=8x³−4x²+2x+4x²−2x+1−(8x³-x-8x²+1)$
$=8x³−4x²+2x+4x²−2x+1−8x³+x+8x²-1$
$=8x²+x$
Câu 2: Tìm x, biết:
$a) (3x-1)(4x+3)-(6x-1)(2x-3)=0$
$⇔12x²+9x-4x-3-(12x²-18x-2x+3)=0$
$⇔12x²+9x-4x-3-12x²+18x+2x-3=0$
$⇔-11x=0$
$⇔x=0$
$b) 9x²-(3x+7)(2x+3)=49$
$⇔9x²−(6x²+9x+14x+21)=49$
$⇔9x²−6x²-9x-14x-21=49$
$⇔3x²−23x−21=49$
$⇔3x²−23x=49+21$
$⇔x(3x-23)=70$
⇔$\left[\begin{matrix} x=70\\ 3x-23=70\end{matrix}\right.$
⇔$\left[\begin{matrix} x=70\\ x=31\end{matrix}\right.$
Chúc bn hc tốt🥰
$\text{#LinhSad}$
