Obtain an expression for the intercept (b) of the straight line (
of form y=mx+b) which is tangent to the parabola y=-(x-c)^2+d, at the point
x=a and touches the parabola at the point y(a).
You may enter a number, an expression such
as 'sqrt()', or an algebraic statement such as '1/exp(3**2 + 4^2)', where
we have explicitly shown that either '**' or '^' may be used as a power.
