cos θ = a^2 + b^2 - c^2
---------------------
2ab
那麼,
sin θ = ??
A
=
= =
=====
= θ =
b = = c
= =
= =
= =
=================
B a C
AB=b
BC=a
AC=c
∠BAC=θ
更新1:
A = = = ====== b = θ = c = = = = ================== B a C AB=b BC=a AC=c ∠BAC=θ