No.
You can do just about anything to pi, and the answer will still be a transcendental number (a special kind of irrational number than can't be the solution of an algebraic equation).
The only thing I can think of is pi/pi =1 (or multiples of this).
Pi X 5 = 15.7. Pi is equal to 3.14 then you multiply it by 5.
No, it is not.
Circumference is 2 times pi times radius, so the circumference of this circle is 2 times pi times 5, or 10 times pi. If a decimal answer is needed, pi is approximately 3.14, so C=31.4
No.
15.7
3.141592654 * 5 = 15.70796327
The formula for a circumference is 2 times Pi times Radius. A diameter is twice the Radius, so the circumference is Diameter times Pi. 5 times Pi (3.14159) is approximately 15.70795. Pi has an endless number of digits to the right of the decimal point, so the best we can do is approximate.
15.072
It is still equal to pi (3.1416) because when you multiply anything by 1 no matter how many times you multiply it, you end up with that other number.
The area of a circle is equal to pi times the radius squared. So in your case it would be 5 squared, (25) times pi which is equal to ~78.5
mass of proton is 6 x pi raised to power 5 times mass of electron
A circle with a end point of 2 times 5 time -1 times -4 would be the divided by pi. This would equal to a circumference of 1.59.