SOLUTION: Which triangle should be solved by beginning with the Law of Cosines? a. A = 115 degrees, a = 19, b = 13 d. A = 62 degrees, B = 15 degrees, b = 10 c. B = 48 degrees, a = 22, b =

Question 341387: Which triangle should be solved by beginning with the Law of Cosines?
a. A = 115 degrees, a = 19, b = 13
d. A = 62 degrees, B = 15 degrees, b = 10
c. B = 48 degrees, a = 22, b = 5
d. A = 50 degrees, b = 20, c = 18
Answer by Theo(13342) (Show Source): You can put this solution on YOUR website!
The law of cosines states that:

c^2 = a^2 + b^2 - 2abCos(C)

or:

a^2 = b^2 + c^2 - 2bcCos(A)

or:

b^2 = a^2 + c^2 - 2acCos(B).

You know the value of 2 sides and the included angle between them.

If you draw a triangle ABC, then side AB is equal to c, side BC is equal to a, and side AC is equal to b.

a is opposite angle A.
b is opposite angle B.
c is opposite angle C.

If a is opposite angle A, then angle A has to be included between sides b and c.
If b is opposite angle B, then angle B has to be included between sides a and c
If c is opposite angle C, then angle C has to be included between sides a and b.

It looks like option D is your choice.

That states that:

A = 50 degrees, b = 20, c = 18

Side a is opposite angle a which means that angle A is included between sides b and c.

Your law of cosines formula would be:

a^2 = b^2 + c^2 - 2bcCos(A).

Draw yourself triangle ABC.

Side a is opposite angle A.
Side b is opposite angle B.
Side c is opposite angle C.

You can see that side a is the unknown sides and that angle A is between the known sides of b and c.
RELATED QUESTIONS
Should the triangle be solved beginning with Law of Sines or Law of cosines. Then solve... (answered by Alan3354)

Should the triangle be solved beginning with Law of Sines, or Laws of Cosines. Then solve (answered by stanbon)

Should the triangle be solved beginning with Law of Sines or Law of cosines. Then solve... (answered by Alan3354)

Should the triangle be solved beginning with Laws of sines or Laws of Cosines. Then... (answered by stanbon)

Should the triangle be solved beginning with Law of Sines or Law of cosines. Then solve... (answered by Alan3354)

I have two questions. 1. Should the traingle be solved with Law of Sines or Laws of... (answered by Alan3354)

Should the triangle be solved beginning with Laws of Sines or Laws of Cosines. Then... (answered by adamchapman)

find angle A of the oblique triangle with sides a=13, b=14, and c=15: find angle A of... (answered by jim_thompson5910)

The sides of a triangle measure 18 in, 25 in, and 36 in. To the nearest degree, what is... (answered by jim_thompson5910,ikleyn)