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\(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-8\)
\(=\)\(\left(x+2\right)\left(x+5\right)\left(x+3\right)\left(x+4\right)-8\)
\(=\)\(\left(x^2+7x+10\right)\left(x^2+7x+12\right)-8\)
Đặt \(x^2+7x+11=t\) ta có :
\(=\)\(\left(t-1\right)\left(t+1\right)-8\)
\(=\)\(t^2-1-8\)
\(=\)\(t^2-9\)
\(=\)\(\left(t-3\right)\left(t+3\right)\)
\(=\)\(\left(x^2+7x+11-3\right)\left(x^2+7x+11+3\right)\)
\(=\)\(\left(x^2+7x+8\right)\left(x^2+7x+14\right)\)
Chúc bạn học tốt ~
a) x4 + 4 = (x4 + 4x2 + 4) - 4x2 = (x2 + 2)2 - 4x2 = (x2 + 2x + 2)(x2 - 2x + 2)
b) (x + 2)(x + 3)(x + 4)(x + 5) - 24 = (x + 2)(x + 5)(x + 3)(x + 4) - 24
= (x2 + 7x + 10)(x2 + 7x + 12) - 24
Đặt x2 + 7x + 10 = y => y(y + 2) - 24 = y2 + 2y - 24
= y2 + 6y - 4y - 24 = (y - 4)(y + 6) = (x2 + 7x + 10 - 4)(x2 + 7x + 10 + 6)
= (x2 + 7x + 6)(x2 + 7x + 16) = (x2 + x + 6x + 6)(x2 + 7x + 16) = (x + 1)(x + 6)(x2 + 7x + 16)
\(x^4+13x^2+36=x^4+4x^2+9x^2+36\)
\(=x^2\left(x^2+4\right)+9\left(x^2+4\right)=\left(x^2+9\right)\left(x^2+4\right)\)
1) \(x^3+x^2+4\)
\(=\left(x^3-x^2+2x\right)+\left(2x^2-2x+4\right)\)
\(=x\left(x^2-x+2\right)+2\left(x^2-x+2\right)\)
\(=\left(x^2-x+2\right)\left(x+2\right)\)
2) \(x^3-2x-4\)
\(=\left(x^3+2x^2+2x\right)-\left(2x^2+4x+4\right)\)
\(=x\left(x^2+2x+2\right)-2\left(x^2+2x+2\right)\)
\(=\left(x^2+2x+2\right)\left(x-2\right)\)
=[(x+2)(x+5)][(x+3)(x+4)]−24=(x2+7x+10)(x2+7x+12)−24=(x2+7x+11)2−1−24=(x2+7x+11)2−25=(x2+7x+11−5)(x2+7x+11+5)=(x2+7x+6)(x2+7x+16)=(x+1)(x+6)(x2+7x+16)
\(x^4+4x^2+4-4x^2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2-2x+2\right).\left(x^2+2x+2\right)\)