a: \(=C^0_5\cdot\left(2x\right)^5+C^1_5\cdot\left(2x\right)^4\cdot\left(3y\right)^1+C^2_5\cdot\left(2x\right)^3\cdot\left(3y\right)^2+C^3_5\cdot\left(2x\right)^2\cdot\left(3y\right)^3+C^4_5\cdot2x\cdot\left(3y\right)^4+C^5_5\cdot\left(3y\right)^5\)
\(=32x^5+240x^4y+720x^3y^2+1080x^2y^3+810xy^4+243y^5\)
b: \(=C^0_6\cdot1^6\cdot\left(-\dfrac{2}{x}\right)^0+C^1_6\cdot\left(-\dfrac{2}{x}\right)^1+C^2_6\cdot\left(-\dfrac{2}{x}\right)^2+C^3_6\cdot\left(-\dfrac{2}{x}\right)^3+C^4_6\cdot\left(-\dfrac{2}{x}\right)^4+C^5_6\cdot\left(-\dfrac{2}{x}\right)^5+C^6_6\cdot\left(-\dfrac{2}{x}\right)^6\)
\(=1-\dfrac{12}{x}+\dfrac{60}{x^2}-\dfrac{160}{x^3}+\dfrac{240}{x^4}-\dfrac{192}{x^5}+\dfrac{64}{x^6}\)
