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 given line is the coefficient of x, 3/5. The slope of the perpendicular line will be the negative reciprocal of that: -1/(3/5) = -5/3.

The point-slope form of the equation for a line of slope m through point (h, k) can be written ...

... y = m(x -h) +k

For your point and the slope found above, this becomes

... y = (-5/3)(x -15) -5

When x=0, this is

... y = (-5/3)(-15) -5 = 20

The y-intercept is 20.