bc and Newton's method, 43 bytes
Newton's method for finding zeros of any function converges quadratically and the algorithm is way simpler than for Gauss-Legendre. It basically boils down to:
So here goes the according snippet:
n=20;x=3;scale=2^n;while(n--)x-=s(x)/c(x);x
A bit more reada...
@Maltysen While the Gauss-Legendre algorithm is really the go-to solution for that problem, it isn't the goal. That said, I do think it'd be a dupe since answers that use the algorithm could be copied without modification.
Now that I’ve given up, I can finally say something I was going to say earlier but couldn’t: You could set yourself a lesser challenge by avoiding the letter T instead of E. It’s the second most common in English.