Question

1.Tính 

a, 5x^3yz . (-7x^2y^3)

b, 6x(x-5) -x(6x+3)

c, (x-9)(x^2-2x-1)

2.Cho A (x)=10-2x+4x^3-5x^2

          B(x)=-10x^3-5x+6x^2-20

Tính A(x)+B(x); A(x)-B(x)

3.Tìm nghiệm

a,M(x)= 5x+20

b,N(x)=100x^2-49

c,P(x)=3x-15

Answer 1

\(1,\\ a,=-35x^5y^4z\\ b,=6x^2-30x-6x^2-3x=-33x\\ c,=x^3-9x^2-2x^2+18x-x+9=x^3-11x^2+17x+9\\ 2,\\ A\left(x\right)+B\left(x\right)=10-2x+4x^3-5x^2-10x^3-5x+6x^2-20\\ =-6x^3+x^2-7x-10\\ A\left(x\right)-B\left(x\right)=10-2x+4x^3-5x^2+10x^3+5x-6x^2+20\\ =14x^3-11x^2+3x+30\\ 3,\\ a,M\left(x\right)=5x+20=0\\ \Leftrightarrow x=-4\\ b,N\left(x\right)=100x^2-49=0\\ \Leftrightarrow\left(10x-7\right)\left(10x+7\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{7}{10}\\x=-\dfrac{7}{10}\end{matrix}\right.\\ c,P\left(x\right)=3x-15=0\\ \Leftrightarrow x=5\)