Bài 5:
a: \(4x^2\left(5x-3y\right)-5x^2\left(4x+y\right)\)
\(=20x^3-12x^2y-20x^3-5x^2y\)
\(=-17x^2y=-17\cdot\left(-2\right)^2\cdot\left(-3\right)=51\cdot4=204\)
b: \(\left(x-4\right)\left(x-2\right)-\left(x-1\right)\left(x-3\right)\)
\(=x^2-2x-4x+8-\left(x^2-3x-x+3\right)\)
\(=x^2-6x+8-x^2+4x-3=-2x+5\)
\(=-2\cdot\frac74+5=-\frac72+5=\frac32\)
Bài 4:
a: 3x+2(5-x)=0
=>3x+10-2x=0
=>x+10=0
=>x=-10
b: \(x\left(2x-1\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)
=>\(\left(2x^2-x\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)
=>\(2x^3+10x^2-x^2-5x-\left(2x^3+9x^2+x+4,5\right)=3,5\)
=>\(2x^3+9x^2-5x-2x^3-9x^2-x-4,5=3,5\)
=>-6x=4,5+3,5=8
=>\(x=-\frac86=-\frac43\)
Bài 3:
a: \(x\left(3x+12\right)-\left(7x-20\right)+x^2\left(2x-3\right)-x\left(2x^2+5\right)\)
\(=3x^2+12x-7x+20+2x^3-3x^2-2x^3-5x\)
=20
b: \(3\left(2x-1\right)-5\left(x-3\right)+6\left(3x-4\right)-19x\)
=6x-3-5x+15+18x-24-19x
=(6x-5x+18x-19x)+(-3+15-24)
=12-24
=-12
