`a)(5x-7y)²`
`=(5x)²-2.5x.7y+(7y)^2`
`=25x²-70xy+49y²`
`b)9x²-6x+1`
`=(3x)²-2.3x.1+1²`
`=(3x-1)²`
`c)25y²-9x²`
`=(5y)²-(3x)²`
`=(5y+3x)(5y-3x)`
`e)(7x+y)(7x-y)`
`=(7x)²-y²`
`=49x²-y²`
`g)x²-1`
`=x²-1²`
`=(x+1)(x-1)`
`h)(x²-2)(x²+2)`
`=(x^2)^2-2²`
`=x^4-4`
`i)16x²+24xy+9y²`
`=(4x)²+2.4x.3y+(3y)²`
`=(4x+3y)²`
`k)(x²+y²)^2`
`=(x^2)^2+2.x².y²+(y^2)^2`
`=x^4+2x²y²+y^4`
`m)(x+y²)(x-y²)`
`=x^2-(y^2)^2`
`=x²-y^4`
`n)(4x²-2y)^2`
`=(4x^2)^2-2.4x².2y+(2y)²`
`=16x^4-16x²y+4y²`
