Câu hỏi của Cry...

Question

Phân tích các đa thức sau thành nhân tử:

a) $-4x^2+12xy-9y^2+25$

b) $\left(3x-1\right)^2-16$

Trần Hải An · Accepted Answer

a) $-4x^2+12xy-9y^2+25$

$=-\left(4x^2-12xy+9y^2\right)+25$

$=-\left[\left(2x\right)^2-2.2x.3y+\left(3y\right)^2\right]+25$

$=-\left(2x-3y\right)^2+25$

$=-\left(2x-3y\right)^2+5^2$

$=5^2-\left(2x-3y\right)^2$

$=\left(5-2x-3y\right)\left(5+2x-3y\right)$

b) $\left(3x-1\right)^2-16$

$=\left(3x-1\right)^2-4^2$

$=\left(3x-1-4\right)\left(3x-1+4\right)$

$=\left(3x-5\right)\left(3x+3\right)$Câu trả lời: a) $-4x^2+12xy-9y^2+25$

$=-\left(4x^2-12xy+9y^2\right)+25$

$=-\left[\left(2x\right)^2-2.2x.3y+\left(3y\right)^2\right]+25$

$=-\left(2x-3y\right)^2+25$

$=-\left(2x-3y\right)^2+5^2$

$=5^2-\left(2x-3y\right)^2$

$=\left(5-2x-3y\right)\left(5+2x-3y\right)$

b) $\left(3x-1\right)^2-16$

$=\left(3x-1\right)^2-4^2$

$=\left(3x-1-4\right)\left(3x-1+4\right)$

$=\left(3x-5\right)\left(3x+3\right)$

Trần Dương · Answer

a ) $-4x^2+12xy-9y^2+25$

$=-\left(4x^2-12xy+9y^2-25\right)$

$=-\left[\left(2x-3y\right)^2-25\right]$

$=-\left(2x-3y+5\right)\left(2x-3y-5\right)$

b ) $\left(3x-1\right)^2-16$

$=\left(3x-1+4\right)\left(3x-1-4\right)$

$=\left(3x+3\right)\left(3x-5\right)$Câu trả lời: a ) $-4x^2+12xy-9y^2+25$

$=-\left(4x^2-12xy+9y^2-25\right)$

$=-\left[\left(2x-3y\right)^2-25\right]$

$=-\left(2x-3y+5\right)\left(2x-3y-5\right)$

b ) $\left(3x-1\right)^2-16$

$=\left(3x-1+4\right)\left(3x-1-4\right)$

$=\left(3x+3\right)\left(3x-5\right)$

Bài 3: Những hằng đẳng thức đáng nhớ