`1)`
`(x+1)^2-(x-1)^2-3(x-1)(x+1)`
`=(x+1-x+1)(x+1+x-1)-3(x^2-1)`
`=4x-3x^2+3`
`2)`
`5(x+2)(x-3)-1/2(6-8x)^2+17`
`=5(x^2-3x+2x-6)-1/2(36-96x+64x^2)+17`
`=5x^2-5x-30-18+48x-32x^2+17`
`=-27x^2+43x-31`
`3)`
`(2x+y)^2-(2x-y)^2`
`=(2x+y-2x+y)(2x+y+2x-y)`
`=2y.4x`
`=8xy`