a: Sửa đề: \(\left(-3x^3+5x^2-9x+15\right):\left(-3x+5\right)\)
\(=\frac{3x^3-5x^2+9x-15}{3x-5}\)
\(=\frac{x^2\left(3x-5\right)+3\left(3x-5\right)}{3x-5}=x^2+3\)
b: Sửa đề: \(\left(5x^4+9x^3-2x^2-4x-8\right):\left(x-1\right)\)
\(=\frac{5x^4-5x^3+14x^3-14x^2+12x^2-12x+8x-8}{x-1}\)
\(=\frac{5x^3\left(x-1\right)+14x^2\left(x-1\right)+12x\left(x-1\right)+8\left(x-1\right)}{x-1}\)
\(=5x^3+14x^2+12x+8\)