To convert degrees to radians, we use the formula:
radians = degrees x π / 180
where π is pi (approximately 3.14159) and 180 is the number of degrees in a half circle (or π radians).
To find the number of radians in 72°, we can substitute this value into the formula:
radians = 72 x π / 180
radians = π / 5
So the answer is D. 2π/5.
Note that none of the answer choices match this result exactly, but D is the closest approximation.