`a)(x-1)(2x-5)`
`=x(2x-5)-1(2x-5)`
`=2x²-5x-2x+5`
`=2x²-7x+5`
`b)(x²-2x-1)(3x+1)`
`=(x²-2x-1).3x+(x²-2x-1).1`
`=3x³-6x²-3x+x²-2x-1`
`=3x³+(-6x²+x²)-(3x+2x)-1`
`=3x³-5x²-5x-1`
`c)(4x+3y)(x²-y²+xy)`
`=4x(x²-y²+xy)+3y(x²-y²+xy)`
`=4x³-4xy²+4x²y+3x²y-3y³+3xy²`
`=4x³-3y³+(-4xy²+3xy²)+(4x²y+3x²y)`
`=4x³-3y³-xy²+7x²y`
`d)2x(2x+3)(x²-1)`
`=(4x²+6x)(x²-1)`
`=4x²(x²-1)+6x(x²-1)`
`=4x^4-4x²+6x³-6x`
