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. Giúp nha
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a) \(a^4+4\)
\(=a^4+4a^2+4-4a^2\)
\(=\left(a^2+2\right)^2+\left(2a\right)^2\)
\(=\left(a^2+2a+2\right)\left(a^2-2a+2\right)\)
b) \(\left(x+y+z\right)^3-x^3-y^3-z^3\)
\(=\left[\left(x+y\right)+z\right]^3-x^3-y^3-z^3\)
\(=\left(x+y\right)^3+z^3+3z\left(x+y\right)\left(x+y+z\right)-x^3-y^3-z^3\)
\(=x^3+y^3+3xy\left(x+y\right)+z^3+3z\left(x+y\right)\left(x+y+z\right)-x^3-y^3-z^3\)
\(=3\left(x+y\right)\left(xy+xz+yz+z^2\right)\)
\(=3\left(x+y\right)\left[x\left(y+z\right)+z\left(y+z\right)\right]\)
\(=3\left(x+y\right)\left(y+z\right)\left(z+x\right)\)
(x80+x40+1)/(x20+x10+1)
=x60+x30
=x30(x2+1)
HIHI ÁNH BÉO TỚ LÀM BỪA 
c)(x2+x)2-2(x2+x)-15
đặt x2+x=a ta có
a2-2a-15
=a2+3a-5a-15
=(a2+3a)-(5a+15)
=a(a+3)-5(a+3)
=(a+3)(a-5)
thay a=x2+x
(x2+x+3)(x2+x-5)
\(\left(x+y+z\right)^2-2\left(x+y+z\right)\left(x+y\right)+\left(x+y\right)^2\)
= \(\left[\left(x+y+z\right)-\left(x+y\right)\right]^2\)
= \(z^2\)
Ta có:(x + y + z)2 - 2(x + y + z) (x + y) + (x + y)2
=[(x+y+z)-(x+y)]2=z2
\(x^4+2014x^2+2013x+2014\)
\(=x^4+2014x^2+2014x-x+2014\)
\(=\left(x^4-x\right)+\left(2014x^2+2014x+2014\right)\)
\(=x\left(x^3-1\right)+2014\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2014\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-x+2014\right)\)
b)\(x^8+7x^4+6\)
\(=x^8+x^4+6x^4+6\)
\(=x^4\left(x^4+1\right)+6\left(x^4+1\right)\)
\(=\left(x^4+1\right)\left(x^4+6\right)\)
b) \(x^8+7x^4+16\)
\(=\left(x^8+8x^4+16\right)-x^4\)
\(=\left[\left(x^4\right)^2+2.x^4.4+4^2\right]-x^4\)
\(=\left(x^4+4\right)^2-\left(x^2\right)^2\)
\(=\left(x^4+4-x^2\right)\left(x^4+4+x^2\right)\)
\(9\left(x-y\right)^2-4\left(x+y\right)^2=\left[3\left(x-y\right)-2\left(x+y\right)\right]\left[3\left(x-y\right)+2\left(x+y\right)\right]\)
\(=\left(3x-3y-2x-2y\right)\left(3x-3y+2x+2y\right)\)
\(=\left(x-5y\right)\left(5x-y\right)\)