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-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)