Đáp án:
Giải thích các bước giải:
`câu.3:`
$a) 2x(x-3y)+3y(2x-5y) = 2x²-6xy+6xy-15y² =2x²-15y²$
$b) (2x-3)(x+2)-(4x-2)(x-5) = 2x²+4x−3x−6−(4x²−20x−2x+10) $
$=2x²+x−6−(4x²−22x+10) = 2x²+x−6−4x²+22x−10 = −2x²+23x−16$
$c) (6x-1)(3+x)+(2x+5)(-3x) = 18x+6x²-3-x−6x²−15x = 2x−3$
$d) 5x(x-1)-(x+2)(5x-7) = 5x²−5x−(5x²−7x+10x−14) = 5x²−5x−(5x²+3𝑥−14) $
$=5x²−5x−5x²−3x+14 = −8x+14$
$e) (x-3)(2x-1)-(x-7)(2x-1) = 2²−x−6x+3−(2x²−x−14x+7) = 2²−x−6x+3−2x²+x+14x-7$
$=8x−4$
$f) 3x(2x-8)+(2x+5)(5-x) = 6x²−24x+10x-2x²+25-5x = 4x²−19x+25$
`câu.4:`
`a) 3(2x-3)+2(2-x)=-3 ⇔ 6x−9+4-2x=-3 ⇔ 4x−5=−3 ⇔ 4x=2 ⇔x=1/2`
`b) x(5-2x)+2x(x-1)=13 ⇔ 5x-2x²+2x²-2x=13 ⇔ 7x=13 ⇔ x=13/7`
`c) 5x(x-1)-(x+2)(5x-7)=6 ⇔ 5x²−5x−(5x²−7x+10x−14)=6 ⇔5x²−5x−(5x²+3x−14)=6`
`⇔5x²−5x−5x²−3x+14=6 ⇔ −8x+14=6 ⇔-8x=6-14 ⇔ -8x=-8 ⇔ x=1`
`d) 3x(2x+3)-(2x+5)(3x-2)=8 ⇔6x²+9x−(6x²−4x+15x−10)=8 ⇔6x²+9x−(6x²+11x−10)=8`
`⇔6x²+9x−6x²−11x+10=8 ⇔ −2x+10=8 ⇔ −2x=-2 ⇔x=1`
`e) 2(5x-8)-3(4x-5)=4(3x-4)+11 ⇔10x−16−12x+15=12x−16+11 ⇔10x-12x-12x=-16+11+16-15`
`⇔-14x=-4 ⇔x=2/7`
`f) 2x(6x-2x²)+3x²(x-4)=8 ⇔12x²-2x³+3x³-12x²=8 ⇔x³=8 ⇔x=8`
chúc bạn học tốt T^T
