a) `(5x-1)(x+3)-(5x+3)(x+5)`
`=5x^2+15x-x-3-5x^2-25x-3x-1`
`=-14x-18`
b) `(1/2-x)^2 = (1/2)^2 - 2. 1/2 .x + x^2 = 1/4 - x +x^2`
c) `(x+3y)^2 = x^2 + 2. x.3y + (3y)^2=x^2+6xy+9y^2`
d) `(2y-x)^3`
`= (2y)^3 - 3.(2y)^2 .x + 3.2y.x^2 - x^3`
`= 8y^3-12xy^2+6x^2y-x^3`