a) \(x^3-8=\left(x-2\right)\left(x^2+2x+4\right)\)
\(9x^2-1=\left(3x-1\right)\left(3x+1\right)\)
b) \(\left(2x-3\right)^2+2\left(4x^2-9\right)+\left(2x+3\right)^2\)
\(=4x^2-12x+9+8x^2-18+4x^2+12x+9\)
\(=16x^2\)
c) \(4x^2-4x+y^2+8y+18>0\)
⇔ \(\left(2x\right)^2-2.2.x+1+y^2+2.4.x+16+1>0\)
⇔\(\left(2x-1\right)^2+\left(y+4\right)^2+1>0\) ( luôn đúng )
1a:
x3 - 8 = x3 - 23 = (x - 2)(x2 + 2x + 22) = (x - 2)(x2 + 2x + 4)
9x2 - 1 = (3x)2 - 12 = (3x)2 - 3x1 + 12 = (3x)2 - 3x1 + 1
câu 2 a) \(15x^2y-12x^2=3x^2\left(5y-4\right)\)
b) \(16-9x^2+6xy-y^2=4^2-\left(3x-y\right)^2=\left(4+3x-y\right)\left(4-3x+y\right)\)
