Solve for x with given equation

I have a problem trying to find the value in this long equation, whats the correct input?

I consider f'c = x so i use syms x

and below my simplified attempt but no result

syms x
3.818=x(1-sqrt(1-(2.809*10^-5*(42/sqrt(x))^2+7.9*10^-3*(42/sqrt(x))-0.0053*(42/sqrt(x))

Incorrect use of '=' operator. Assign a value to a variable using '=' and compare values for equality using '=='.

Answer 1

[Alan Stevens]

Look up the help on function fzero.

And don't forget that Matlab doesn't recognise implicit multiplication. x(...) should be x*(...)