1. The problem statement, all variables and given/known data f(x)=20+25*sin(0.85x) x = number of hours from start. f(x) = temperature. For how long is the temperature negative (under 0) during the first 10 hours? We haven't learned how to derive/integrate trig equations so that is out of the question. 2. Relevant equations 3. The attempt at a solution Most people with similar problems have said they used their graph calculator to solve these kinds of questions. I tried figuring out the period (7.39) and took the half of that + the remaining 2.61 but during those there is no more under the graph. So the answer would seem to be around 3.7 but it is only 1.5. How do I use my graph calculator (TI-84) to solve this?