已知圆的半径是4cm,弦AB=4根号2,则弦AB的中点M到弦AB所队的劣弧中点N的距离是

已知圆的半径是R=4cm,弦L=4*2^0.5,则弦AB的中点M到弦AB所队的劣弧中点N的距离是H?
弧所对的圆心角为A.
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((4*2^0.5/2)/4)
=90度
H=R-R*COS(A/2)
=4-4*COS(90/2)
=1.172cm