Patrick B. answered 10/26/20
Math and computer tutor/teacher
sin(0) = 0
sin(pi/2) = 1
the slope of the secant line is (1-0) / ( pi/2-0)
= 1 / (pi/2) = 2/pi
derivative is cosx ---> cos c = 2/pi
c = inverse_cos(2/pi)
= 0.8806892354203566672269437825689
and 0 < c < pi/2