Question

Given x+y=2,express x^2-2y-4 in terms of y?

Answer 1

x+y=2
⇒x = 2-y

x² - 2y - 4
= (2-y)² - 2y - 4 
= (4 + y² - 4y) - 2y - 4
= 4 + y² - 4y - 2y - 4
= y² - 6y

Answer 2

x+y=2
x=2-y
so substitute it
x^2-2y-4
=(2-y)^2-2y-4
=4+y^2-4y-2y-4
=y^2-6y
if u take y common
=y(y-6)
thats it