When the equation you’re solving on your TI84 Plus calculator has multiple solutions, it’s sometimes helpful to redefine the bound variable. Trigonometric functions are notorious for having infinite number of solutions. Often, a question will ask for the solutions within a certain interval. Adjusting the bound variable at the bottom of the screen ensures that you will only find solutions that are in the interval defined by the bound variable.
Follow these steps to redefine the bound variable:

Use the arrow keys to place the cursor anywhere in the line containing the bound variable:

Press [CLEAR] to erase the current entry.

Press [2nd][(] to insert the left brace.

Enter the lower bound, press [,], enter the upper bound, and then press [2nd][)] to insert the right brace.

Press [ENTER] to store the new setting in the bound variable, or press the uparrow key to make your guess.
Here is a typical question you might see:
Find all the real solutions to the function Y = 3*sin(2X + 1), where 0 < X < π.
Enter the equation into E1. Change the bounds following the preceding steps. See the first screen.
Guess a number close to the lower bound. You can see the resulting solution of guessing 0.3 in the second screen.
Now, guess a number close to the upper bound. Guessing 3 finds another solution, as shown in the third screen.
If the variable you’re solving for is assigned a value (guess) that isn’t in the interval defined by the bound variable, then you get the ERR: BAD GUESS error message.