A triangle has sides A, B, and C. The angle between sides A and B is π3. If side C has a length of 4 and the angle between sides B and C is 3π8, what are the lengths of sides A and B?

1 Answer
Mar 8, 2016

A=4.27
B=3.66

Explanation:

This is a mult-step problem. Now, conventionally, a side length is denoted by a lowercase letter, rather than an uppercase one like in the problem above. Still, I don't want to confuse anyone, so I'll write the problems in the same way as it is given. We do need to label the angles though, so I'm going to say that 3π8 is signified by x, and π3 by z, with the remaining angle called y.

So, I don't want to deal with the angles given in radians. I want to cahnge the angles from radians to degrees, and to do that it is a simple conversion. If we begin with 3π8, and multiply it by 3602π, then we have 1080π16π. The πs divide out, and that leaves us with 67.5o.

So that's one angle converted, one to go.

π33602π gives us 60o.

So now we know that C=4, z=60, and x=67.5.
Because all the angles in a triangle must add up to 180, we can take the whole, 180, and subtract 67.5 and 60 from it. That leaves us with 52.5, which equals y.

I'm going to solve for A using the law of sines, like this:
Asinx=Csinz. After we fill in the variables with what we know, we have Asin67.5=4sin60, which simplifies to A=4.267.

Now we just need to solve for B.
Bsiny=Csinz. This becomes Bsin52.5=4sin60, and can be simplified to B=3.664.

Now we're done. Nice job!