Explanation:
the slope of a line is always the factor of x.
here : 1/2
it is the ratio y/x indicating how many units y changes, when x changes a certain angina amount of units when going from one point to another.
a perpendicular slope puts x and y upside-down and flips the sign.
here : -2/1 = -2
so, the equation looks like
y = -2x + b
b is the y-intercept, and we get this by putting the x and y coordinates of the given point into this equation and solve for b :
-1 = -2×-2 + b
-1 = 4 + b
b = -5
the full equation is therefore
y = -2x - 5