Solve a quadratic with trigonometric values in degrees

[Carsen]

The past replies are pointing you in the right direction. The equation solver is the best tool for the job on the 50g because your problem is asking for a numerical answer. If the equation solver doesn't work or spits out an error, enter a guess for the variable you are solving for and try again. It will find the answer closest to that guess.

However...

You can use SOLVE, SOLVEVX, & ZEROS to find the solutions as well. These functions are known as CAS (computer algebraic system) functions. Typically, to use CAS functions...

1. The calculator needs to be in radian mode
2. The calculator needs to be in exact mode. See the equals sign by R= in the header? You need that = sign.
3. The equation must have no decimal points in them. If they have decimal points in them, press [white shift] [ 6 ] REWRITE [ NXT] ->Q. This command will take the whole equation & convert decimals to fractions.
   

In order to understand the above, here are the steps used to solve your problem d*cos(30) = 25*sqrt(d/9.81) with the SOLVE command. I am assuming you are in RPN mode.

1. Look at the image attached & make sure the 50g's header has RAD & '=' displayed.
2. Type 'D*COS(30) = 25*SQRT(D/9.81)' and press ENTER
3. Now press [white shift] [ 6 ] REWRITE [ NXT ] ->Q.
4. Type 'D'. Then use the PURGE command.
5. Type 'D'. Then use the SOLVE command. You should get { D=62500/(981*COS(30)^2) D=0 }
6. Press [white shift] [ EVAL ] TYPE OBJ->
7. Get D=62500/(981*COS(30)^2) on level 1 of the stack & put the 50g in degree mode
8. Press [down arrow] [down arrow] [backspace] [backspace] [backspace] [orange shift] [ENTER]. It should say 84.9473326539.
   

A lot of work huh! This really shows that the equation solver is the best tool for the job. This calculator is hard to learn BUT once you get it, you'll cut through problems like a hot knife through butter.

If you have questions, let me know.