Câu 2:
a: \(\left(x-4\right)^2-9\)
=(x-4-3)(x-4+3)
=(x-1)(x-7)
b: \(5x+5y-x^2-2xy-y^2\)
\(=5\left(x+y\right)-\left(x+y\right)^2\)
=(x+y)(5-x-y)
c: \(x^2+4x-5\)
\(=x^2+5x-x-5\)
=x(x+5)-(x+5)
=(x+5)(x-1)
d: \(x^4+4=x^4+4x^2+4-4x^2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2-2x+2\right)\left(x^2+2x+2\right)\)
Bài 1:
a: \(A=x\left(4-x\right)+\left(x-2\right)^2\)
\(=4x-x^2+x^2-4x+4\)
=4
b: \(B=\left(x+5\right)^2-\left(x-5\right)^2\)
\(=x^2+10x+25-\left(x^2-10x+25\right)\)
\(=x^2+10x+25-x^2+10x-25\)
=20x
c: \(C=\left(x-2\right)\left(2x+3\right)-2x\left(x-1\right)-\left(x-10\right)\)
\(=2x^2+3x-4x-6-2x^2+2x-x+10\)
=-6+10
=4
d: \(D=\left(x+y\right)^3-3xy\left(x+y\right)-x^3+y^3\)
\(=x^3+y^3+3xy\left(x+y\right)-3xy\left(x+y\right)-x^3+y^3\)
\(=2y^3\)
