16(x-y)^2-25(x+y)^2

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16(x-y)^2-25(x+y)^2
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16(x-y)^2-25(x+y)^2
16(x-y)^2-25(x+y)^2

16(x-y)^2-25(x+y)^2
=[4(x-y)]^2-[5(x+y)]^2
=(4x-4y)^2-(5x+5y)^2
=(4x-4y+5x+5y)(4x-4y-5x-5y)
=(9x+y)(-x-9y)
=-(9x+y)(x+9y)

16(x-y)^2-25(x+y)^2
=[4(x-y)+5(x+y)][4(x-y)-5(x+y)]
=(9x+y)(-x-9y)
=-(9x+y)(x+9y)