-x + 2y = 4
2y = x + 4
y = 1/2x + 2.....slope here is 1/2. A perpendicular line will have a negative reciprocal slope. All that means is " flip " the slope and change the sign. So the slope we need is -2 (see how I flipped the slope and changed the sign)
y = mx + b
slope(m) = -2
(-2,1)...x = -2 and y = 1
now we sub and solve for b, the y int
1 = -2(-2) + b
1 = 4 + b
1 - 4 = b
-3 = b
so ur perpendicular line is : y = -2x - 3
