a/ $3x(2-x)+\left(3x-\dfrac34\right)2x$
$= 6x-3x^2+6x^2-\dfrac32 x$
b/ `3x(x-2)-7x(1+x)-4(4-x^2)`
`= 3x^2-6x-7x-7x^2-16+4x^2`
`= -13x-16`
c/ `(x+1)(x^2+2x-1)`
`= x^3+2x^2-x+x^2+2x-1`
`= x^3+3x^2+x-1`
d/ `(x+y)^2+(x-y)^2`
`= x^2+2xy+y^2+x^2-2xy+y^2`
`= 2x^2+2y^2`
e/ `2(x-5)(x+5)+(x+5)^2+(x-5)^2`
`= (x+5+x-5)^2`
`= 4x^2`
