`5) 1/2x^3y (2x^4y^3 - 4xy - 6)`
`= x^7y^4 - 2x^4y^2 - 3x^3y`
`6) -5/6x (2/3x^2y + 3/4xy^2 - 1/2xy)`
`= -5/9x^3y - 5/8x^2y^2 + 5/12x^2y`
`7) x^4y^5(7/3x^2y^4 - 1/7x^3y - 5/14)`
`= 7/3x^6y^9 - 1/7x^7y^6 - 5/14x^4y^5`
`8) (3x + 5)(2x - 7)`
`= 6x^2 - 21x + 10x - 35`
`= 6x^2 + (-21x + 10x) - 35`
`= 6x^2 - 11x - 35`
`9) (-5x +2)(-3x - 4)`
`= 15x^2 + 20 - 6x - 8`
`= 15x^2 - 6x + (20 - 8)`
`= 15x^2 - 6x + 12`
`10) (x - 5)^2 - (4x - 3)(2 - x)`
`= x^2 - 10x + 25 - (8x - 4x^2 - 6 + 3x)`
`= x^2 - 10x + 25 - 8x + 4x^2 + 6 - 3x`
`= (x^2 + 4x^2) + (-10 - 8x - 3x) + (6 + 25)`
`= 5x^2 - 21x + 31`
