How to plot in Mathcad 15

The first line in your sheet specifies an equation.

The second line gives an equation, to solve, but to solve for what?

The third line factors an expression.

The fourth line gives an equation to be rewritten.

The plot: You did not define the function b(a), so there's nothing to plot.

You can define b(a), related to the equation with:

Success!

Luc