Question 984922
For very small values of theta (in radians), sin(x) approximately equals x. 
The first five terms of the Taylor series expansion for sin(x) is 
{{{sin(x)=x-x^3/3!+x^5/5!-x^7/7!+x^9/9!}}}
So when x is small, {{{x^3}}} and higher order terms become insignificant to the final answer.
You just have to define what small means in your case.