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\(2x\left(x^2-7x-3\right)=2x^3-14x-6x\)
\(4xy^2\left(-2x^3+y^2-7xy\right)=-8x^4y^2+4xy^5-28x^2y^3\)
a: \(=15x^4-12x^3+9x^2\)
c: \(=5x^3-15x^2-4x^2+12x\)
\(=5x^3-19x^2+12x\)
a) \(=\dfrac{x+15}{\left(x-3\right)\left(x+3\right)}+\dfrac{2}{x+3}=\dfrac{x+15+2\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}=\dfrac{3x-9}{\left(x-3\right)\left(x+3\right)}=\dfrac{3\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}=\dfrac{3}{x+3}\)
b) \(=\dfrac{x+y}{2\left(x-y\right)}-\dfrac{x-y}{2\left(x+y\right)}+\dfrac{y^2+x^2}{\left(x-y\right)\left(x+y\right)}=\dfrac{\left(x+y\right)^2-\left(x-y\right)^2+2\left(x^2+y^2\right)}{2\left(x-y\right)\left(x+y\right)}=\dfrac{2\left(x^2+y^2+2xy\right)}{2\left(x-y\right)\left(x+y\right)}=\dfrac{\left(x+y\right)^2}{\left(x-y\right)\left(x+y\right)}=\dfrac{x+y}{x-y}\)
\(a,=27x^3+27x^2+9x+1\)
\(b,=\dfrac{x^3}{27}-\dfrac{x^2}{3}+x-1\)
\(c,=-\left(27x^3-27x^2y^2+9xy^4-y^6\right)\)
\(=-27x^3+27x^2y^2-9xy^4+y^6\)
\(d,=\dfrac{x^3}{y^3}-\dfrac{6x}{y}+\dfrac{12y}{x}-\dfrac{8y^3}{x^3}\)
a) \(\left(3x+1\right)^3=27x^3+27x^2+9x+1\)
b) \(\left(\dfrac{x}{3}-1\right)^3=\dfrac{x^3}{27}-\dfrac{x^2}{3}\)
c) \(\left(-y^2+3x\right)^3=27x^3-27x^2y^2+9xy^4-y^6\)
d) \(\left(\dfrac{x}{y}-\dfrac{2y}{x}\right)^3=\dfrac{x^3}{y^3}-\dfrac{6x}{y}+\dfrac{12y}{x}-\dfrac{8y^3}{x^3}\)