bài 1:
\(2x^2\left(3x^3+2x\right)\)
\(=2x^2\cdot3x^3+2x^2\cdot2x\)
\(=6x^5+4x^3\)
\(3x\left(x^2+2x+2\right)=3x\cdot x^2+3x\cdot2x+3x\cdot2=3x^3+6x^2+6x\)
\(\left(3x+3\right)\left(6x^2+2x+3\right)\)
\(=18x^3+6x^2+9x+18x^2+6x+9\)
\(=18x^3+24x^2+15x+9\)
\(\left(5x+4\right)\left(3x-1\right)\)
\(=15x^2-5x+12x-4\)
\(=15x^2+7x-4\)
\(\left(x-1\right)\left(x+1\right)\)
\(=x^2-1^2\)
\(=x^2-1\)
\(2x^2\left(x^3-x^2+1\right)+4x\left(x^4-2x^3+1\right)\)
\(=2x^5-2x^4+2x^2+4x^5-8x^4+4x\)
\(=6x^5-10x^4+2x^2+4x\)
\(x^3\left(1+2x^2-4x\right)+3x^3\left(3-x\right)\)
\(=x^3+2x^5-4x^4+9x^3-3x^4\)
\(=2x^5-7x^4+10x^3\)
bài 2:
\(B=4x^2\cdot\left(x^2+4x+2\right)\)
\(=4x^2\cdot x^2+4x^2\cdot4x+4x^2\cdot2\)
\(=4x^4+16x^3+8x^2\)
Khi x=1/2 thì \(B=4\cdot\left(\dfrac{1}{2}\right)^4+16\cdot\left(\dfrac{1}{2}\right)^3+8\cdot\left(\dfrac{1}{2}\right)^2\)
\(=4\cdot\dfrac{1}{16}+16\cdot\dfrac{1}{8}+8\cdot\dfrac{1}{4}\)
\(=\dfrac{1}{4}+2+2=4,25\)