Finding an angle when three sides are given

King E

New member
Consider a ΔABC.

The three sides given are:

AB = 8cm

AC = 15cm

BC = 17cm

The angle required is ∠A.

If I apply Pythagoras theorem, that is BC² = AB² + AC² in this case, then I come to know that it is a right angle.

Is there a way to find ∠A without using the Pythagoras theorem BC² = AB² + AC² ?

Subhotosh Khan

Super Moderator
Staff member
Have you learned Law of Cosines of a triangle?

Jomo

Elite Member
You can also use Heron's formula to find the area and hence the length AD. Then you can find the two angles which make up <A.