1: cross m as the vertical MD of AB, connecting CD and SD. With MD//= 1/2AP. = "MD is perpendicular to the surface ABC, =" MD is perpendicular to SN. And AC = 1/2ab = "ad = ab. So < ADB=45. There are SD= 1/2AB and ND=NA= 1/2AB. So < DNS=45. (It can be deduced that the length of NS is two-thirds of the root sign, which is used in the second question. ) So there is a CD perpendicular to NS. So NS is perpendicular to the surface CDM, so CM is perpendicular to SN.

2. According to: V(M-CNS)=V(S-CMN), we can find the distance from point S to plane CMN and the length of NS from the first question. The angle can be expressed by trigonometric function.