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

Question

please help me! this is an important test.

Answer 1

Okay,  the equation of a line is y= mx + b (m = slope, b = y-intercept)

the line y = x + 10 has slope (m) of 1.

You need a line perpendicular to that line. So the slope needs to be the "negative reciprocal" of that slope.

Therefore you need the slope to be -1/1 which equals -1.

So now you have y = -x + b.

To find the y-intercept (or "b"), just substitute the point (15,-5) into the equation and solve for b.

-5 = -15 + b

b = 10

y = -x + 10