Solve the following equations calculate the error$\%$:

a$.\frac{x^2}{2-x}=1\mathrm{.}8{10}^{-5}($solve as a quadratic equation$)$

b$.\frac{x^2}{2-x}=1\mathrm{.}8{10}^{-5}($solve as a quadratic equation ignoring the $x$ in denominator$)$

c$.$ calculate the error$\%($answer from a is the true value$)$