00:02
This question is about the law of signs.
00:05
It asks us to solve this triangle.
00:10
Now, to solve right angle to triangles, of course, we can't use pythagorean theorem or trig ratios directly, because those only work for right -angled triangles.
00:28
For non -right -angled triangles, we have to either use the law of signs or the law of cosines.
00:34
Now, the law of signs is simpler, so you should try to use that whenever you can.
00:38
And i can tell you when that is.
00:42
The law of cosines should only be used when you are given just the three side lengths or just two side lengths and the angle in between them.
00:54
Only in those cases do you need to use the cosine law or the law of cosines.
00:59
In all other cases, as long as you're given enough information, you can solve using the law of signs.
01:06
Okay, now we get on with a question.
01:09
We want to find the values of c, the angle, beta, and gamma, where beta and gamma are angles, and c is a side length.
01:22
And the law of science, recall, looks like this.
01:44
Now, how do we use that to find one of these three quantities? well, first of all, we need to know, well, to use one equation, we need to know three of the four quantities so that we can find the fourth.
02:01
And so we need to know one pair and an additional piece of information.
02:06
So aside an angle pair, such as a and alpha, and either one other side length or one other angle.
02:17
Now, if we take a look, we don't have the beta b pair because beta is unknown.
02:23
We don't know the gamma -c pair because neither of them are known.
02:27
We only have, the only known pair is the a alpha pair...