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D = x2 - 4x - y2 - 8y - 12
= (x2 - 4x + 4) - (y2 + 8y + 16)
= (x - 2)2 - (y + 4)2
= (x + y + 2)(x - y - 6)
\(D=x^2-4x-y^2-8y-12\)
\(=x^2-4x-y^2-8y+4-16\)
\(=\left(x^2-4x+4\right)-\left(y^2+8y+16\right)\)
\(=\left(x-2\right)^2-\left(y+4\right)^2\)
\(=\left(x-2-y-4\right)\left(x-2+y+4\right)\)
\(=\left(x-y-6\right)\left(x+y+2\right)\)
5x2 + 10xy - 4x - 8y
= 5x(x + 2y) - 2(x - 2y)
= (5x - 2)(x + 2y)
=(5x2 + 10xy) - (4x + 8y) = 5x.(x + 2y) - 4.(x + 2y) = (5x - 4).(x + 2y)
Theo bài ra , ta có :
4x2 - 4xy + 8y2
= (2x)2 - 2.2xy + y2 + 7y2
= (2x + y)2 + 7y2
Chúc bạn hôc tốt =))
\(4xy-4x^2-y^2+16\)
\(=16-\left(4x^2-4xy+y^2\right)\)
\(=16-\left(2x-y\right)^2\)
\(=\left(4+2x-y\right)\left(4-2x+y\right)\)
\(4x^2-4x-y^2-8y-15\)
\(=\left(4x^2-4x+1\right)-\left(y^2+8y+16\right)\)
\(=\left(2x-1\right)^2-\left(y+4\right)^2\)
\(=\left(2x+y+3\right)\left(2x-y-5\right)\)
\(4x^2-4x-y^2-8y-15\)
\(=\left(4x^2-4x-1\right)-\left(y^2-8y-16\right)\)
\(=\left(4x^2-4x-1\right)-\left(y^2+8y+16\right)\)
\(=\left[\left(2x\right)^2-4x-1\right]-\left[y\left(y+8\right)\right]+16\)
\(=\left(2x^2-6x\right)\left(y+12\right)\left(y-4\right)\)
...
\(4x^2-y^2+8x-16\)
\(=\left(2x\right)^2-\left(y-4\right)^2=\left(2x-y+4\right)\left(2x+y-4\right)\)
4x2 - y2 + 8y - 16
= 4x2 - (y2 - 8y + 16)
= (2x)2 - (y - 4)2
= [2x - (y - 4)][2x + (y - 4)]
= (2x - y +4)(2x + y - 4)