Given x + y = 2, then expressing x2-2y-4 in terms of y gives
y2-6y-8
y2-6y
y2-6y-2
y2+4y
x=2-y
so x2-2y-4 = (2-y)2-2y-4 = y2-6y
If 2x – 3y = 1, then express 4x2−2x+3 in terms of y.