Store x coordinate of a solution

Questions
1

Hi, I want to solve a polynomial eqn f(x) = a and store the x coordinate of the solution for use in another expression, can I do this without explicitly writing out an expression for x in terms of f inv and a?

The matlab equivalent would be the first element of y = solve(f, x) where f = … == a

2

Desmos doesn’t solve anything for you. You might be able to use some large lists and best fit a factored form to estimate, but I don’t think it would be as exact as explicitly defining your solutions.