a)\(\frac{3y}{4x}+\frac{5y}{4x}=\frac{3y+5y}{4x}=\frac{8y}{4x}=\frac{2y}{x}\)

b)\(\frac{x^2+1}{2x-4}-\frac{7x}{2-x}=\frac{x^2+1}{2\left(x-2\right)}-\frac{-7x}{x-2}\)

\(=\frac{x^2+1}{2\left(x-2\right)}-\frac{-7x\times2}{\left(x-2\right)\times2}=\frac{x^2+1+14x}{2\left(x-2\right)}\)

a: \(=\dfrac{4x-2+6x^2-6x+2x^2+1}{2x\left(2x-1\right)}=\dfrac{8x^2-2x-1}{2x\left(2x-1\right)}\)

c: \(=\dfrac{x^3+2x+2x^2+2x+x^2-x+1}{\left(x+1\right)\left(x^2-x+1\right)}\)

\(=\dfrac{x^3+3x^2+3x+1}{\left(x+1\right)\left(x^2-x+1\right)}=\dfrac{x^2+2x+1}{x^2-x+1}\)

\(\dfrac{1}{x-3}-\dfrac{1}{x}=\dfrac{x-\left(x-3\right)}{x\left(x-3\right)}=\dfrac{x-x+3}{x\left(x-3\right)}=\dfrac{3}{x\left(x-3\right)}\)

\(B=\dfrac{1}{x^2-3x}+\dfrac{1}{x^2-9x+18}+\dfrac{1}{x^2-15x+54}+\dfrac{1}{x^2-21x+108}\)

\(=\dfrac{1}{x\left(x-3\right)}+\dfrac{1}{\left(x-3\right)\left(x-6\right)}+\dfrac{1}{\left(x-6\right)\left(x-9\right)}+\dfrac{1}{\left(x-9\right)\left(x-12\right)}\)

\(=\dfrac{1}{3}\left(\dfrac{3}{x\left(x-3\right)}+\dfrac{3}{\left(x-3\right)\left(x-6\right)}+\dfrac{3}{\left(x-6\right)\left(x-9\right)}+\dfrac{3}{\left(x-9\right)\left(x-12\right)}\right)\)

\(=\dfrac{1}{3}\left(-\dfrac{1}{x}+\dfrac{1}{x-3}-\dfrac{1}{x-3}+\dfrac{1}{x-6}-\dfrac{1}{x-6}+\dfrac{1}{x-9}-\dfrac{1}{x-9}+\dfrac{1}{x-12}\right)\)

\(=\dfrac{1}{3}\left(-\dfrac{1}{x}+\dfrac{1}{x-12}\right)\)

\(=\dfrac{1}{3}\cdot\dfrac{-\left(x-12\right)+x}{x\left(x-12\right)}\)

\(=\dfrac{4}{x\left(x-12\right)}\)

Thực hiện phép tính

a,  6x³y⁵z : 3xy³z=2x²y²

b,  \(\frac{3x+6}{x+2}+\frac{2x+4}{x+2}\)

\(=\frac{3\left(x+2\right)}{x+2}+\frac{2\left(x+2\right)}{x+2}\)

=3+2=5

1) \(-6x^4+4x^3-2x^2\)

2) \(=x^2+4x-21-x^2-4x+5=-16\)

3) \(=6x^2-4x-x^2-4x-4=5x^2-8x-4\)

4) \(=2x^3-4x^2-8x-3x^2+6x+12=2x^3-7x^2-2x+12\)

giúp mình với

\(a,=-21x^3+28x^2y\\ b,=5x^2-4x-15x+12=5x^2-19x+12\\ c,=4x^2-4x+1\\ d,=49-x^2\)