As we know the formula to calculate the line of equation is y - y1 = m (x - x1)
Where m is the slope. y1 is the first y co ordinate. x1 is the first x co ordinate.
Now we do know that the slope of perpendicular line is the negative reciprocal of the slope of the original line.
So perpendiculars line slope is -1/2 so slope for our line is 2. Hence equation is y - 2 = 2 (x -1) which becomes y = 2x.
