用余弦定理.a²=b²+c²-2bc cos A
44²=30²+44.5²-2X30X44.5Xcos A
cos A=（30²+44.5²-44²）/2X30X44.5
=（900+1980.25-1936）/2670
=944.25/2670
=0.35365168539325842696629213483146.
A=69.289168095820380877195163243031.°
=69°17.350085749222852631709794581842.‘
=69°17’21.005144953371157902587674910526.“