I am very new to maths so I would appreciate if posters are patient with me as this is a learning curve
I have a triangle with no equal sides and I am looking to find angle B. The length of the sides I will make up as 12cm, 22cm and 28cm.
I know all three sides and none of the angles and I am thinking that I should be using the cosine rule, therefore I have completed the following;
C2 = a2 + b2 – 2ab cos Ø
122 = 222 + 282 – 2 · 22 · 28 cos Ø
144 = 484 + 784 – 1232 cos Ø
144 = 1268 – 1232 cos Ø
1232 cos Ø = 1124
Cos Ø = 1124
Cos Ø = 0.91
Cos -1 Ø = 24.2º (1dp)
Have I used the right rule, if not please advise why, and if I have would you please advise why I can't use the Sine Rule and what the difference is?