9(x-5y)²-49(x+5y)²

9(x-5y)²-49(x+5y)²
9(x-5y)²-49(x+5y)²

9(x-5y)²-49(x+5y)²
9(x-5y)²-49(x+5y)²
=[3(x-5y)]²-[7(x+5y)]²
=[3(x-5y)+7(x+5y)][3(x-5y)-7(x+5y)]
=(3x-15y+7x+35y)(3x-15y-7x-35y)
=(10x-20y)(-4x-50y)
=-20(x-2y)(2x+25y)

9（x^2-10xy+25y^2）-49(x^2+10xy+25y^2)
=18x^2-90xy+225y^2-49x^2-490xy-1225y^2
=-31x^2-580xy-1000y^2