00:01
Alright, so there's lots going on here.
00:04
I'm gonna do all of the first problem and then leave you with diagrams for the rest of them, and hopefully you can use those first ones to help you with the diagrams.
00:14
So we've got a triangle abc.
00:17
We're told that angle a is 65 degrees, angle b is 35 degrees, and side ab is 7.
00:23
So we're gonna sketch that out.
00:25
There's our triangle, and it's abc.
00:27
So we've got angle abc, angle a is 65 degrees, angle b is 35 degrees, and side ab is 7, which means that little c is 7.
00:39
It's the side opposite angle c.
00:42
So for this one, since we have two angles and the side included between them, we're gonna need to use the law of cosines.
00:51
So the easiest way to think about law of cosines is to notice that the side that you...
01:03
The a squared and the cosine of a are both on the outside.
01:07
That's the way i like to think about it.
01:09
So we know...let's see.
01:15
No, actually we can use law of sines here.
01:18
Yeah, we can use law of sines here because we know that if this is 65 degrees, if this is 35 degrees, that's 110.
01:32
No, that's 100.
01:34
So this one must be 80 degrees.
01:36
So now we can use law of sines.
01:38
That makes it much easier.
01:41
So angle c is 80 degrees, and then we're gonna just use the law of sines, which says that the sine of any angle over the side opposite that angle is equal to the sine...
01:56
The ratio of the sine of any other angle across...over the side across from it, sine of c over c.
02:04
So we can just say this is side a, this is side b.
02:09
So we can say we know the sine of...we know sine of c is sine of 80.
02:16
C is 7.
02:17
Sine of 65 over a.
02:22
Sine of 35 over b.
02:26
So we can first solve for a using these two ratios.
02:32
Sine of 65 over a equals sine of 80 over 7.
02:39
And then you take the cross products.
02:48
A times the sine of 80 degrees equals 7 times the sine of 65 degrees.
02:56
Divide both sides by the sine of 80 degrees, and you get a equals 7 sine 65 divided by sine 80.
03:09
So we're going to go to the calculator.
03:11
I need to make sure i'm in degree mode.
03:16
7 sine 65.
03:20
All of that divided by sine of 80.
03:31
765 sine of 80.
03:36
And that's 6 and 4 tenths, or 6 and 44 hundredths.
03:51
I'm not sure how you're supposed to round.
03:54
That would be to the nearest tenth.
03:56
This would be to the nearest hundredth.
04:00
So that's the first one.
04:05
Second one, we're going to work the exact same way.
04:08
We know we've got triangle def.
04:13
We know angle d is 73 degrees.
04:16
The side opposite that, side d is 14.
04:19
Side f is 10.
04:21
So we can first find angle f.
04:25
So sine of f over 10 equals sine of 73 over 14.
04:37
So then we have 14 sine of f equals 10 times 73.
04:53
Divide both sides by 14.
04:56
We get the sine of f is equal to 10 sine 73 over 14.
05:07
So we take the inverse sine of both sides, and that leaves us with f equals the inverse sine of 10 sine 73 over 14.
05:30
So 10 sine 73 over 14.
05:34
So we need the inverse sine 10 sine 73 over 14.
05:52
That gives us 43 and 1 tenth.
06:02
So angle f is 43 and 1 tenth.
06:09
We'll just round it to the nearest whole number 43 degrees, which means angle e has got to be, add these two together and you get 116.
06:19
So angle e must be 180 minus 116, which is 64.
06:39
And now we need to find side e.
06:41
So we can use any one.
06:46
We've got everything we need now.
06:48
Let's see.
06:49
F is 43 degrees.
06:52
E is 64 degrees.
06:55
So then we can use sine of 64 over e equals sine of 73 over 14.
07:08
So then we have e sine 73 equals 14 sine 64.
07:27
Divide both sides by sine of 73, and you get e equals 14 sine 64.
07:38
Divide it by the sine of 73...