Cosine Rule Help (1 Viewer)

[superbird]

I know the cosine rule is (b^2 + c^2 - a^2)/2bc
the thing is how do i determine what's a,b or c.

sometimes i get a wrong answer simply for using the wrong number for b or a etc.

should i take it that c is the largest side and a is the smallest?

 

[DeadFish]

I know the cosine rule is (b^2 + c^2 - a^2)/2bc
the thing is how do i determine what's a,b or c.

sometimes i get a wrong answer simply for using the wrong number for b or a etc.

should i take it that c is the largest side and a is the smallest?

NO.

For finding an unknown angle, b and c are the sides that "forms" the angle. a is the one that is "opposite" to the angle.

 

[JamiL]

a^2=b^2+c^2 -2bc*cosA
a is the side opp to the angle A its not a matter of bigger or smaller, depend on information. u should realy no this by now. not studyin 4 it 2 day b4 ur exam

 

[xeriphic]

you a,b,c are non-captalised which represent the sides, which A,B,C represent the angles

for each angle, ie. A, the side which is opposite facing the angle would be a, likewise for b,B and c,C pairs