已知三角形三边的长,求三个角的度数.(几何公式忘光了)

[vansoft]

比如:a=3,b=4,c=5的三角形

求出AB夹角,BC夹角,AC夹角的度数公式.

[verywzm]

a*a + b*b + c*c -(cosC)*a*b =0

[hl7865063]

我也不知道，但是你要是给我一个夹角的度数的话，我会给出你其他两个角的度数嘎嘎

[vansoft]

COS(X)=0.75
怎么求出X的值？

[verywzm]

反余弦函数：Inverse Cosine（）

[northwolves]

Function ANGLE(ByVal a As Double, ByVal b As Double, ByVal c As Double)
ANGLE = (b * b + c * c - a * a) / (2 * b * c)
ANGLE = Atn(-ANGLE / Sqr(1 - ANGLE * ANGLE)) + 2 * Atn(1)
ANGLE = ANGLE * 45 / Atn(1) & "°"
End Function
Sub GETANGLES(ByVal a As Double, ByVal b As Double, ByVal c As Double)
Dim x(6) As String
x(0) = "IF a=" & a
x(1) = " b=" & b
x(2) = " c=" & c
x(3) = "Then"
x(4) = "∠ABC=" & ANGLE(b, c, a)
x(5) = "∠BAC=" & ANGLE(a, b, c)
x(6) = "∠ACB=" & ANGLE(c, a, b)
MsgBox Join(x, vbCrLf)
End Sub
Private Sub Command1_Click()
GETANGLES 3, 4, 5
End Sub

[verywzm]

好象错了
反余弦函数：Arccos(X) = Atn(-X / Sqr(-X * X + 1)) + 2 * Atn(1)

[verywzm]

啊，这也错了a*a + b*b -c*c -(cosC)*a*b =0，晕

[northwolves]

COS(X)=0.75
怎么求出X的值？


Function arccos(ByVal x As Double) As String
arccos = 2 * Atn(1) - Atn(x / Sqr(1 - x * x))
arccos = arccos / (4 * Atn(1))
arccos = arccos & "π"
End Function

Private Sub Command1_Click()
MsgBox arccos(0.5)
End Sub

[verywzm]

今天头晕掉，不好意思有写错了a*a + b*b -2*(cosC)*a*b =c*c