知道三角形三边长度 怎么求任意角的角度？

Question

左边为30CM 右边为44.5CM 底为40CM 求左下角的角度~

Answer 1

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......“追问

我都不会算~~什么COS 什么意思？反正不会是Cosplay的意思~嘿嘿~~
我找了个高材生 算出来是77.5度~

追答

对不起，是我错了。左下角应该是：
44.5²=30²+40²-2X30X40Xcos A
cos A=（30²+40²-44.5²）/2X30X40
=（900+1600-1980.25）/2400
=519.75/2400
=0.2165625
A=77.492788098165015771615245978092......°
=77°29.567285889900946296914758685522......‘
=77°29’34.037153394056777814885521131326......”