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\(-4x^2+12xy-9y^2+25=25-\left(2x-3y\right)^2=\left(5-2x+3y\right)\left(5+2x-3y\right)\)
a/25-9y^2-4x^2+12xy
=-(9y^2-12xy+4x^2-25)
=-[(3y)^2-2.3y.2x+(2x)^2-5^2]
=-[(3y-2x)^2-5^2]
=-(3y-2x-5)(3y-2x+5)
b/4x^2-8xy+4y^2-5x+5y
=4(x^2-2.x.y+y^2)-5(x-y)
=4(x-y)^2-5(x-y)
=(x-y)(4x-4y-5)
a) \(9\left(a+b\right)^2-4\left(a-2b\right)^2\)
\(=\left[3\left(a+b\right)+2\left(a-2b\right)\right]\left[3\left(a+b\right)-2\left(a-2b\right)\right]\)
\(=\left(3a+3b+2a-4b\right)\left(3a+3b-2a+4b\right)\)
\(=\left(5a-b\right)\left(a+7b\right)\)
b) \(\left(2a-b\right)^2-4\left(a-b\right)^2\)
\(=\left[\left(2a-b\right)-2\left(a-b\right)\right]\left[\left(2a-b\right)+2\left(a-b\right)\right]\)
\(=\left(2a-b-2a+2b\right)\left(2a-b+2a-2b\right)\)
\(=b\left(4a-3b\right)\)
c) \(125-\left(x+2\right)^3\)
\(=\left(5-x-2\right)\left[25+5\left(x+2\right)+\left(x+2\right)^2\right]\)
\(=\left(3-x\right)\left(25+5x+10+x^2+4x+4\right)\)
\(=\left(3-x\right)\left(x^2+9x+39\right)\)
d) \(\left(x+3\right)^3-8=\left(x+3-2\right)\left[\left(x+3\right)^2+2\left(x+3\right)+4\right]\)
\(=\left(x+1\right)\left(x^2+8x+19\right)\)
e) \(x^{12}-y^4=\left(x^6\right)^2-\left(y^2\right)^2=\left(x^6-y^2\right)\left(x^6+y^2\right)\) 9 khai triển tiếp hđt 6,7)
\(27y^3-9y^2+y-\frac{1}{27}\)
\(=\left(3y\right)^3-3.\left(3y\right)^2.\frac{1}{3}+3.3y.\left(\frac{1}{3}\right)^2-\left(\frac{1}{3}\right)^3\)
\(=\left(3y-\frac{1}{3}\right)^3\)
hk
tốt
Lời giải:
a.
$x^4+10x^3+26x^2+10x+1$
$=(x^4+10x^3+25x^2)+x^2+10x+1$
$=(x^2+5x)^2+2(x^2+5x)+1-x^2$
$=(x^2+5x+1)^2-x^2=(x^2+5x+1-x)(x^2+5x+1+x)$
$=(x^2+4x+1)(x^2+6x+1)$
b.
$x^4+x^3-4x^2+x+1$
$=(x^4-x^2)+(x^3-x^2)+(x-x^2)+(1-x^2)$
$=x^2(x-1)(x+1)+x^2(x-1)-x(x-1)-(x-1)(x+1)$
$=(x-1)[x^2(x+1)+x^2-x-(x+1)]$
$=(x-1)(x^3+2x^2-2x-1)$
$=(x-1)[(x^3-1)+(2x^2-2x)]=(x-1)[(x-1)(x^2+x+1)+2x(x-1)]$
$=(x-1)(x-1)(x^2+x+1+2x)=(x-1)^2(x^2+3x+1)$
\(9x^6-12x^7+4x^8\)
\(=x^6\left(4x^2-12x+9\right)\)
\(=x^6.\left(2x-3\right)^2\)
hk
tốt
\(x^4-x^2+2x-1\)
\(=x^4-\left(x^2-2x+1\right)\)
\(=x^4-\left(x-1\right)^2\)
\(=\left(x^2-x+1\right)\left(x^2+x-1\right)\)
hk
tốt
a: \(ab+a+b+1\)
\(=a\left(b+1\right)+\left(b+1\right)\)
\(=\left(b+1\right)\left(a+1\right)\)
c: \(4x^2-12xy+3x-9y\)
\(=4x\left(x-3y\right)+3\left(x-3y\right)\)
\(=\left(x-3y\right)\left(4x+3\right)\)
\(=-2x^2+6xy-3y^2+25\)
\(=-\left(2x^2-6xy+3y^2\right)+25\)
\(=-\left(2x^2+3y^2\right)+25\)
\(=\left(2x^2-3y^2\right)+25\)
\(=\left(2x^2+3y^2\right).\left(2x^2-3y^2\right)+25\)
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