Phân tích thành nhân tử : \(2x^2+7x+5\)
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\(a,=5x^2-5x+3x-3=\left(x-1\right)\left(5x+3\right)\\ b,=2x^2-5x+2x-5=\left(2x-5\right)\left(x+1\right)\\ c,=x^2+5x-3x-15=\left(x+5\right)\left(x-3\right)\\ d,=7x^2-7x+x-1=\left(x-1\right)\left(7x+1\right)\)
a: Ta có: \(-3x^4+20x^3-35x^2-10x+48\)
\(=-\left(3x^4-20x^3+35x^2+10x-48\right)\)
\(=-\left(3x^4-9x^3-11x^3+33x^2+2x^2-6x+16x-48\right)\)
\(=-\left(x-3\right)\left(3x^3-11x^2+2x+16\right)\)
\(=-\left(x-3\right)\left(3x^3-6x^2-5x^2+10x-8x+16\right)\)
\(=-\left(x-3\right)\left(x-2\right)\left(3x^2-5x-8\right)\)
\(=-\left(x-3\right)\left(x-2\right)\left(3x-8\right)\left(x+1\right)\)
b: Ta có: \(-\left(2x^4+7x^3+x^2-7x-3\right)\)
\(=-\left(2x^4-2x^3+9x^3-9x^2+10x^2-10x+3x-3\right)\)
\(=-\left(x-1\right)\left(2x^3+9x^2+10x+3\right)\)
\(=-\left(x-1\right)\left(2x^3+2x^2+7x^2+7x+3x+3\right)\)
\(=-\left(x-1\right)\left(x+1\right)\left(2x^2+7x+3\right)\)
\(=-\left(x-1\right)\left(x+1\right)\cdot\left(x+3\right)\left(2x+1\right)\)
\(2x^4+7x^3-2x^2-13x+6\)
\(=2x^4+6x^3+x^3+3x^2-5x^2-15x+2x+6\)
\(=2x^3\left(x+3\right)+x^2\left(x+3\right)-5x\left(x+3\right)+2\left(x+3\right)\)
\(=\left(2x^3+x^2-5x+2\right)\left(x+3\right)\)
\(=\left(2x^3+4x^2-3x^2-6x+x+2\right)\left(x+3\right)\)
\(=\left[2x^2\left(x+2\right)-3x\left(x+2\right)+\left(x+2\right)\right]\left(x+3\right)\)
\(=\left(2x^2-3x+1\right)\left(x+2\right)\left(x+3\right)\)
\(=\left(2x^2-2x-x+1\right)\left(x+2\right)\left(x+3\right)\)
\(=\left[2x\left(x-1\right)-\left(x-1\right)\right]\left(x+2\right)\left(x+3\right)\)
\(=\left(2x-1\right)\left(x-1\right)\left(x+2\right)\left(x+3\right)\)
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\(-2x^4-7x^3-x^2+7x+3\)
\(=-2x^3\left(x+1\right)-5x^2\left(x+1\right)+4x\left(x+1\right)+3\left(x+1\right)\)
\(=-\left(x+1\right)\left(2x^3+5x^2-4x-3\right)\)
\(=-\left(x+1\right)\left[2x^2\left(x-1\right)+7x\left(x-1\right)+3\left(x-1\right)\right]\)
\(=-\left(x+1\right)\left(x-1\right)\left(2x^2+7x+3\right)\)
\(=-\left(x+1\right)\left(x-1\right)\left(x+3\right)\left(2x+1\right)\)
= 2x^2 + 2x +5x+5
=(2x^2+2x)+(5x+5)
=2x(x+1)+5(x+1)
=(x+1)(2x+5)
\(2x^2+7x+5=2x^2+2x+5x+5\)
\(=2x\left(x+1\right)+5\left(x+1\right)\)
\(=2\left(x+1\right)\left(x+\frac{5}{2}\right)=\left(x+1\right)\left(2x+5\right)\)