A rectangular lamina ABCD has sides AB=CD=2a and BC=AD=a . The midpoint of CD is M and the midpoint of BM is N . THe lamina is folded along BM such that the planes BMC and BMDA are perpendicular . For this folded lamina , find in terms of surds if necessary .

(a) AN

(b) AC

(c) angle ACB

This is what i did :

(a) BM =

,

, AB=2a

AM=AB=2a , cos angle MBC

angle MBC=45 degree , therefore ABN= 45 degree

(b) AMC=90 degree

MC=a , AM = 2a

(c) ABC=90

tan angle ACB = 2a/a

ACB=arctan 2

= 63 degree 26 mins

CAn somepne pls check my working . Thanks a lot !!