Answer:
Step-by-step explanation:
x²+4xy+4y²-8x-16y-20=(x+2y)²-8(x+2y)-20
put x+y=t
t²-8t-20=t²-10t+2t-20=t(t-10)+2(t-10)=(t-10)(t+2)
substitute the value of t
x²-4xy+4y²-8x-16y-20=(x+2y-10)(x+2y+2)
i don't know what else you want.
