Question

What is the y-intercept of the equation of the line that is perpendicular to the line y = 3/5x + 10 and passes through the point (15, –5)?

Answer 1

The slope of the perpendicular line is the negative reciprocal of that of the given line, so is
-1/(3/5) = -5/3
Then the point-slope equation of the perpendicular line can be written as
y = (-5/3)(x -15) -5
y = (-5/3)x +20

The y-intercept of the perpendicular line is y=20.