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\(x^3-4x^2-12x+27=\left(x^3+27\right)-\left(4x^2+12x\right)\)\(=\left(x+3\right)\left(x^2-3x+9\right)-4x\left(x+3\right)\\ =\left(x+3\right)\left(x^2-3x+9-4x\right)=\left(x+3\right)\left(x^2-7x+9\right)\)
\(x^3-4x^2-12x+27\)
\(=x^3+3x^2-7x^2-21x+9x+27\)
\(=x^2\left(x+3\right)-7x\left(x+3\right)+9\left(x+3\right)\)
\(=\left(x+3\right)\left(x^2-7x+9\right)\)
a, x2-7x-14y+2x
=x(x+2)-7(x-2y)
b, x3-4x2y+4xy2-25x
=x3-4x2y+4xy2-y3-25x+y3
=(x-y)3-25x+y3
a ) = x(x+2) - 7(x+2y)
b) = -4 xy ( x-y) + (x^3-25x) [ câu này mk , chaqcs là làm đúng đâu ]
a ) \(x^2-8x+15\)
\(=x^2-3x-5x+15\)
\(=x\left(x-3\right)-5\left(x-3\right)\)
\(=\left(x-3\right)\left(x-5\right)\)
b ) \(4x^8+1\)
\(=4x^8+1+4x^2-4x^2\)
\(=\left(2x^2+1\right)^2-\left(2x\right)^2\)
\(=\left(2x^2+1+2x\right)\left(2x^2+1-2x\right)\)
a) \(x^4+4\)
\(=\left(x^2\right)^2+2\cdot x^2\cdot2+2^2-2\cdot x^2\cdot2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2-2x+2\right)\left(x^2+2x+2\right)\)
b) \(4x^8+1\)
\(=\left(2x^4\right)^2+2\cdot2x^4\cdot1+1^2-2\cdot2x^4\cdot1\)
\(=\left(2x^4+1\right)-\left(2x^2\right)^2\)
\(=\left(2x^4-2x^2+1\right)\left(2x^4+2x^2+1\right)\)
a/ \(x^4+4=\left(x^2\right)^2+4x^2+4-4x^2=\left(x^2+2\right)^2-4x^2=\left(x^2-4x+2\right)\left(x^2+4x+2\right)\)
b/ \(4x^8+1=\left(2x^4\right)^2+1=\left(2x^4\right)^2+4x^4+1-4x^4=\left(2x^4+1\right)^2-4x^2=\left(2x^4-2x+1\right)\left(2x^4+2x+1\right)\)
\(a^5+b^5-\left(a+b\right)^5=a^5+b^5-\left(a^5+5a^4b+10a^3b^2+10a^2b^3+5ab^4+b^5\right)\)( tam giác Pascal )
\(=5a^4b+10a^3b^2+10a^2b^3+5ab^4=5ab\left(a^3+2a^2b+2ab^2+b^3\right)\)
\(=5ab\left(\left(a^3+b^3\right)+\left(2a^2b+2ab^2\right)\right)=5ab\left(\left(a+b\right)\left(a^2-ab+b^2\right)+2ab\left(a+b\right)\right)\)
\(=5ab\left(a+b\right)\left(a^2+ab+b^2\right)\)
a) \(x^4+4\)
\(=\left(x^2\right)^2+2\cdot x^2\cdot2+2^2-2\cdot x^2\cdot2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2-2x+2\right)\left(x^2+2x+2\right)\)
b) \(4x^8+1\)
\(=\left(2x^4\right)^2+2\cdot2x^4\cdot1+1^2-2\cdot2x^4\cdot1\)
\(=\left(2x^4+1\right)^2-\left(2x^2\right)^2\)
\(=\left(2x^4-2x^2+1\right)\left(2x^4+2x^2+1\right)\)
\(x^4+4\)
\(=\left(x^2\right)^2+2.x^2.2+2^2-2.x^2.2\)
\(=\left(x^2+2\right)^2-4x^2\)
\(=\left(x^2+2+2x\right)\left(x^2+2-2x\right)\)
\(4x^8+1\)
\(=\left(2x^4\right)^2+1\)
\(=\left(2x^4\right)^2+4x^4+1-4x^4\)
\(=\left(2x^4+1\right)^2-\left(2x^2\right)^2\)
\(=\left(2x^4+1-2x^2\right)\left(2x^4+1+2x^2\right)\)
\(4\times^8+1\)
\(=4\times^8+2\cdot2\times^4\cdot1+1-2\cdot2\times^4\cdot1\)
\(=\left(2\times^4+1\right)^2-\left(2\times^2\right)^2\)
\(=\left(2\times^4+1-2\times^2\right)\left(2\times^4+1+2\times^2\right)\)