Area of a circle
Use A = πr² to find the area of a circle with radius 5.
The area of a circle is π times the radius squared. With radius 5: A = π × 25 = 78.54 (rounded). The circumference is 2πr, which is about 31.42 here.
Classic Graphing 84
Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.
Press 2nd and the ^ key for π. Multiply by 5 squared.
2ndπ^×5x²Press enter.
enter
You should seeπ*5² 78.53981634
Natural Scientific 991
Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.
Press SHIFT and the ×10ˣ key for π. Multiply by 5 squared and press =. The exact answer is 25π.
SHIFTπ×10ˣ×5x²=Press S⇔D for the decimal.
S⇔D
You should see78.53981634
Classic CAS
Start on the main screen: Press home to open the Home menu (Calculator, Graphs, Settings, and more). Choose Calculator, or press esc to go back to the calculation page.
Press the π key, multiply by 5 squared and press enter. The exact answer 25π is shown.
π×5x²enterUse ctrl then enter to get the decimal answer.
ctrl≈enter
You should see25·π
Press ctrl + enter on a new line with the same input to see 78.5398.
Classic Scientific 30
Start on the main screen: Press 2nd then mode (QUIT) to leave any menu or screen and return to the calculation screen.
Press the π key, multiply, type 5 and press x². Press enter to see 25π.
π×5x²enterPress the fraction-decimal toggle to see the decimal value.
◄►
You should see78.53981634
RPN Scientific 15
Start on the main screen: There is no menu to leave. Press the back arrow to clear a number you are typing, or CLx (g then back arrow) to clear the X register.
Key in 5 and square it with g then x².
5gx²√xPress g then π (above the EEX key) and multiply.
gπEEX×
You should see78.5398
Tips
- If you know the diameter, halve it first. Squaring the diameter gives an area four times too large.
- Use the π key, not 3.14, for a more accurate answer.