因式分解：x²-y²-3x-5y-4

因式分解：x²-y²-3x-5y-4
因式分解：x²-y²-3x-5y-4

因式分解：x²-y²-3x-5y-4
原式=(x+y)(x-y)-3x-5y-4
x+y 1
×
x-y -4
所以原式=(x+y+1)(x-y-4)

X^2-Y^2-3Y-5Y-4
=(X-Y)(X+Y)-3X-5Y-4
=[(X-Y)(X+Y)]-[3X+5Y]-4
=[(X+Y)+1]*[(X-Y)-4]
=(X+Y+1)*(X-Y-4)
题目中用到的是十字相乘法