Write and equation in standard form of the line that passes through (0,a) and (b,0) where a≠0 and b≠0.

Y=mx+b
slope = rise/run = (0-a)/(b-0) = -a/b
y=(-a/b)x + B     (where B is the y-intercept, not b from the point (b,0)
Substitute one of the point into the equation to solve for B.
(0,a)→     a = (-a/b)0 + B
                a = B
So rewrite the equation to be:
y=(-a/b)x + a

The answer is -pie over 2