The argument rad must be expressed in radians and must be a valid numeric expression. Cos by default returns a double unless a single or integer is specified as the return value.
Example
Sub Main()
Dim J As Double
Dim I As Single ' Declare variables.
Dim K As Integer
For I =1 To 10
Msg = Msg & Cos(I) & ", " ' Cos function call
J=Cos(I)
Print J
K=Cos(I)
Print K
Next I
MsgBox Msg ' Display results.
MsgBox Msg1
End Sub