Factorise by splitting the middle term:-

Question

x^2-120xy-625y^2

Answer 1

625 factors into 5 * 5 * 5 * 5. You have to combine the above factors, so the difference will equal 120.

5 * 5 * 5 = 125

125 - 5 = 120, or even better 5 - 125 = -120

Therefore x^2-120xy-625y^2 = (x+5y)(x-125y)

Although this may not be the process you were seeking, I hope this helps. Thanks for asking.