How to get a numeric answer from a equations of sin/cos?

[yma16]

The equations are

cos2x=7/19 and y=[(cosx)^2-(sinx)^2]^-1

Find y.

I'd like to get 19/7 or 2.7... as the answer of y using TI-89. I put them in solve()|0<x<90 with the degree mode. It dose not give me these answers.

Thanks a lot.

[expressbeat]

You have to enter both equations and solve simulatenously for x and y. Set mode to Exact first. In the Home screen, type:

solve(cos(2x)=7/19 and y=((cos(x)^2-sin(x)^2))^(-1),{y,x})

Then:

F2>Approx([your answer])

y=2.7143 (scroll right to see it)

look on google how to solve simulataneous equations on the Ti-89. You have to separate your equations with " and " and for the variable to solve for, enter the variables enclosed in curly brackets and separated with commas. Example:

solve(y=f(x) and z=f(y) and x=f(z),{x,y,z})

Also, don't use the Numeric Solver app - it's pretty pointless.

[yma16]

If you try to use approx(solve(..)), usually it gives you the same result as you use them separately. Not in this problem.