Bài 3:
a: \(C=2\left(x-2\right)\left(x+3\right)-x\left(5x-4\right)+3x\left(x-2\right)+7\)
\(=2\left(x^2+3x-2x-6\right)-5x^2+4x+3x^2-6x+7\)
\(=2\left(x^2+x-6\right)-2x^2-2x+7\)
\(=2x^2+2x+12-2x^2-2x+7=19\)
=>C không phụ thuộc vào biến
b: \(D=x\left(3x-1\right)-x^2\left(x+3\right)+\left(x-1\right)\left(x^2+x+2\right)\)
\(=3x^2-x-x^3-3x^2+\left(x^3+x^2+2x-x^2-x-2\right)\)
\(=-x^3-x+\left(x^3+x-2\right)\)
=-2
=>D không phụ thuộc vào biến
Bài 2:
a: \(\left(2x-3\right)\left(x-2\right)-x\left(2x+1\right)-6=0\)
=>\(2x^2-4x-3x+6-2x^2-x-6=0\)
=>-8x=0
=>x=0
b: \(5\left(2x-1\right)\left(x+2\right)-2\left(5x-3\right)\left(x+2\right)=5\)
=>\(5\left(2x^2+4x-x-2\right)-2\left(5x^2+2x-3x-6\right)=5\)
=>\(5\left(2x^2+3x-2\right)-2\left(5x^2-x-6\right)=5\)
=>\(10x^2+15x-10-10x^2+2x+12=5\)
=>17x+2=5
=>17x=3
=>\(x=\frac{3}{17}\)
c: \(2x^2+3\left(x-2\right)\left(x+2\right)-5x\left(x+3\right)=0\)
=>\(2x^2+3\left(x^2-4\right)-5x^2-15x=0\)
=>\(-3x^2-15x+3x^2-12=0\)
=>-15x-12=0
=>15x=-12
=>\(x=-\frac{12}{15}=-\frac45\)
