Press the "Mode" button on your calculator. Press the "Down" arrow key twice to highlight the "Angle Measure" option.
Press the "+/-" key to switch between angle measurement modes. Select the "Degrees" option, then press the "OK" button to return to the entry screen.
Press the "Alpha" key, followed by the "Forward" key (above the "on" key), followed by the "6" key, to create an angle symbol in the entry screen.
Enter the number "90" after the angle symbol. A right angle is now expressed on your calculator.