trig
posted by sam .
Find all solutions to the equation
2cos(2x) = x + 1, correct to 4 decimal places.

2 cos(2x) never gets out of the range [2,2]
So, whenever x+1 > 2, there are no solutions.
That means all solutions are in [3,1]
A little NewtonRaphson should work nicely here, or a bisection method.