1) \(5x^2\left(3xy^3-x^2y+5y^4\right)=15x^3y^3-5x^4y+25x^2y^4\)
2) \(\left(3x-1\right)\left(1+3x\right)-\left(3x+2\right)^2=9x^2-1-8-9x^2-12x-4=-12x-13\)
3) \(\left(6x^3-7x^2-x+2\right):\left(2x+1\right)=\left[3x^2\left(2x+1\right)-5x\left(2x+1\right)+2\left(2x+1\right)\right]:\left(2x+1\right)=\left[\left(2x+1\right)\left(3x^2-5x+2\right)\right]:\left(2x+1\right)=3x^2-5x+2\)


