Đáp án:
$1)
a)10x+10\\
b)
28xy-7x^2+xy^2-7x^2y+4y^2+7x\\
c)
x^3-x^2y-x^2+xy+3x-3y\\
d)
10x^3-11x^2-11x-2\\
2)
a)
x=\dfrac{36}{19}\\
b)
x=\dfrac{3}{5}\\
c)
x=1$
Giải thích các bước giải:
$1)
a)3x^2-2x(-5+1,5x)+10\\
=3x^2-2x(-5+\dfrac{3}{2}x)+10\\
=3x^2+10x-2x.\dfrac{3}{2}x+10\\
=3x^2+10x-3x^2+10\\
=10x+10\\
b)
7x(4y-x)+xy(y-7x)-2(2y^2-3,5x)\\
=7x.4y-7x.x+xy.y-xy.7x-2.2y^2+2.3,5x\\
=28xy-7x^2+xy^2-7x^2y+4y^2+2.\dfrac{7}{2}x\\
=28xy-7x^2+xy^2-7x^2y+4y^2+7x\\
c)
(x^2-x+3)(x-y)\\
=x^2.x-x^2.y-x.x+x.y+3.x-3.y\\
=x^3-x^2y-x^2+xy+3x-3y\\
d)
(2x^2-3x-1)(5x+2)\\
=2x^2.5x+2x^2.2-3x.5x-3x.2-1.5x-1.2\\
=10x^3+4x^2-15x^2-6x-5x-2\\
=10x^3-11x^2-11x-2\\
2)
a)
3(2x-1)-5(x-3)+6(3x-4)=24\\
\Leftrightarrow 6x-3-5x+15+18x-24-24=0\\
\Leftrightarrow 19x-36=0\\
\Leftrightarrow x=\dfrac{36}{19}\\
b)
2x^2+3(x^2+1)=5x(x+1)\\
\Leftrightarrow 2x^2+3x^2+3=5x^2+5x\\
\Leftrightarrow 5x^2+3-5x^2-5x=0\\
\Leftrightarrow 5x=3\\
\Leftrightarrow x=\dfrac{3}{5}\\
c)
(3x-1)(2x+7)-(x+1)(6x-5)=16\\
\Leftrightarrow 6x^2+21x-2x-7-(6x^2-5x+6x-5)=16\\
\Leftrightarrow 6x^2+21x-2x-7-6x^2+5x-6x+5=16\\
\Leftrightarrow 18x-2=16\\
\Leftrightarrow 18x=18\\
\Leftrightarrow x=1$
