Question

Use a graphing calculator to solve the equation in the interval from 0 to 2pi. Round to the nearest hundredth.

Answer 1

On your calculator, make sure you're in radian mode, not degree mode, that you are in a trig coordinate plane (do this by hitting "zoom" and choosing ZTrig), and when you enter the function into the "y =", you have to enter it in like this:  7cos(2x)-3.  Hit "graph" and you'll see that the wave goes through the x-axis in 4 places within your specified interval.  Hit 2nd and "trace" and then "zero".  Move your cursor so it's just above the x-axis where the curve goes through and hit enter, then move it so it's just below the x-axis where the curve goes through and hit enter again.  Hit enter a 3rd time, and you SHOULD see that your x has a value while y = 0.  Do that for all of the places where the curve goes through the x-axis. That's how you find the zeros of a trig curve (or any curve, for that matter) on a calculator.  The zeros are the solutions. If this was solvable like a regular equation, using trig identities and right triangles, you wouldn't have to use your calculator.  But just like when you go to factor a second degree polynomial and you're having trouble with it you can use the quadratic formula and it's never-fail, neither is your calculator.