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\(x^4+4=\left(x^2\right)^2+2^2\)
\(=\left(x^2+2\right)^2-2.x^2.2=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2+2x+2\right)\left(x^2-2x+2\right)\)
81x^4+4
=(9x^2)^2+36x^2+2^2-36x^2
=(9x^2)^2+36x^2+2^2-(6x)^2
=(9x^2+2)^2-(6x)^2
=(9x^2+2-6x)(9x^2+2+6x)
81x4 + 4 = ( 9x2)2 + 2 2 = ( 9x2)2 + 36x2 + 22 - 36x2 = (9x2 + 2)2 - (6x)2 = (9x2 + 2 - 6x)(9x2 + 2 + 6x)
XONG
\(A=n^4-n^3-6n^2+7n-21\)
\(A=n^4-3n^3+2n^3-6n^2+7n-21\)
\(A=n^3\left(n-3\right)+2n^2\left(n-3\right)+7\left(n-3\right)\)
\(A=\left(n^3+2n^2+7\right)\left(n-3\right)\)
\(A=n^4-n^3-6n^2+7n-21\)
\(A=n^4-3n^3+2n^3-6n^2+7n-21\)
\(A=n^3\left(n-3\right)+2n^2\left(n-3\right)+7\left(n-3\right)\)
\(A=\left(n^3+2n^2+7\right)\left(n-3\right)\)
\(4x^4+y^4\)
\(=\left(2x^2+y^2\right)^2-\left(2xy\right)^2\)
\(=\left(2x^2+y^2+2xy\right)\left(2x^2+y^2-2xy\right)\)
\(x^5+x^4+2\)
\(=x^5+x^4+x^2-x^2+1+1\)
\(=\left(x^5-x^2\right)+\left(x^4+x^2+1\right)\)
\(=\left(x^5-x^2\right)+\left(x^4+2x^2-x^2+1\right)+1\)
\(=x^2\left(x^3-1\right)+\left(x^4+2x^2-x^2+1\right)+1\)
\(=x^2\left(x-1\right)\left(x^2+x+1\right)+\left(\left(x^2+1\right)^2-x^2\right)+1\)
\(=x^2\left(x-1\right)\left(x^2+x+1\right)+\left(x^2+1+x\right)\cdot\left(x^2+1-x\right)+1\)
\(=\left(x^3-x^2\right)\left(x^2+x+1\right)+\left(x^2+1+x\right)\cdot\left(x^2+1-x\right)+1\)
\(=\left(x^2+x+1\right)\left(x^3-x^2+x^2+1-x\right)+1\)
\(=\left(x^2+x+1\right)\left(x^3+1-x\right)+1\)
\(x^4+64\)
\(=\left(x^2\right)^2+8^2+2x^2.8-2x^2.8\)
\(=\left(x^2+8\right)^2-\left(4x^2\right)\)
\(=\left(x^2-4x+8\right)\left(x^2+4x+8\right)\)
\(x^8+3x^4+4\)
\(=x^8+4x^4+4-x^4\)
\(=\left(x^4-2\right)^2-x^4\)
\(=\left(x^4-x^2-2\right)\left(x^4-x^2-2x^2-2\right)\)
\(=\left(x^2-2\right)\left(x^2+1\right)\left(x^2-1\right)\left(x^2+2\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(x^2-2\right)\left(x^2+1\right)\left(x^2+2\right)\)
\(x^4+3x^2-4\)
\(=x^4+4x^2-x^2-4\)
\(=x^2\left(x^2+4\right)-\left(x^2+4\right)\)
\(=\left(x^2+4\right)\left(x^2-1\right)\)
\(=\left(x^2+4\right)\left(x-1\right)\left(x+1\right)\)
Chúc bạn học tốt.
\(x^4+y^4\)
= \(\left(x^2\right)^2+\left(y^2\right)^2+2x^2y^2-2x^2y^2\)
= \(\left(x^2+y^2\right)^2-2x^2y^2\)
= \(\left(x^2+y^2-\sqrt{2}xy\right)\left(x^2+y^2+\sqrt{2}xy\right)\)
Chúc bạn học tốt !!!
Bài làm
x4 + y4
= ( x2 )2 + 2x2y2 + ( y2 )2 - 2x2y2
= [ ( x2 )2 + 2x2y2 + ( y2 )2 ] - 2x2y2
= ( x2 + y2 )2 - 2x2y2
= ( x2 + y2 )2 - ( \(\sqrt{2}xy\))2
= ( x2 + y2 - \(\sqrt{2}xy\))( x2 + y2 + \(\sqrt{2}xy\))
# Học tốt #
ta có :
\(n^4+4=n^4+4n^2+4-4n^2\)
\(=\left(n^2+2\right)^2-4n^2=\left(n^2-2n+2\right)\left(n^2+2n+2\right)\)