TheChosenOne
23rd November 2006, 07:46 PM
Hello All,
I used to make a seriously daft and careless mistake while using the cosine rule so i though i would share it:
Error Example:
Imagine triangle ABC with:
Length AB = 3
Length AC = 4
Angle BAC = 90°
a = b + c - 2bcCosA°
BC = AB + AC -2(ABxAC)CosBAC
BC = 9 + 16 - 24 CosBAC
:mad: Error Below: :eek:
BC = (1)CosBAC
:) It Should Be :cool:
BC = 25
Bc = 5
The error is made when you do: (b + c - 2bc) CosA
The correct was is to do: b + c -(2bcCosA)
Thank you and good luck
P.S. If you feel need more convincing that the answer is incorrect - it is a right angled (3,4,5) traingle.
I used to make a seriously daft and careless mistake while using the cosine rule so i though i would share it:
Error Example:
Imagine triangle ABC with:
Length AB = 3
Length AC = 4
Angle BAC = 90°
a = b + c - 2bcCosA°
BC = AB + AC -2(ABxAC)CosBAC
BC = 9 + 16 - 24 CosBAC
:mad: Error Below: :eek:
BC = (1)CosBAC
:) It Should Be :cool:
BC = 25
Bc = 5
The error is made when you do: (b + c - 2bc) CosA
The correct was is to do: b + c -(2bcCosA)
Thank you and good luck
P.S. If you feel need more convincing that the answer is incorrect - it is a right angled (3,4,5) traingle.