Question

In right triangle ABC, with right angle at C, a= 28 and B= 21 find Sin A/2

In right triangle DEF with right angle at F D= 16 E= 12 find Cos (2E)

I don't get it? Do I just do Cos 24?

Answer 1

so its just as simple as I thought it is?

Answer 2

So is it .18?

Answer 3

and .91?

Answer 4

i misread the question - its not sin A but sin A/2
i'll have to think about this one...

Answer 5

you can easily find the measure of sides b and c and angles A by using the trig ratios.
and there is a trig identity for sin A/2 which i'd have to look up.

Answer 6

Ah geez I don't have the measure of angle b but side B
Can't I just assume those angles are 45 degrees?

Answer 7

And it's also the sides of DEF.

Answer 8

the usual notation is small letters a, b and c are sides (opposite angles A, B and C)
so B = 21 means angle B = 21 degrees
so is that what the question says or should side b = 21?

Answer 9

so side b = 21 right?

Answer 10

No I was an idiot and typed it all up wrong.

Answer 11

I'm given the sides yes.

Answer 12

I'm sorry I meant.
a/ sin A = b/Sin B = c/Sin C

Answer 13

Err no nevermind I don't have side c.

Answer 14

i'm afraid you've lost me moth

Answer 15

Forget everything I said. I was wondering if it was possible to get the correct angle using the law of sines.

Answer 16

is it angle A you want to find?

Answer 17

Yes.

Answer 18

Or I could use the law of cosines to get side c
c² = b² + a² - 2ba cosC
Then use the law of sines to get the appropriate angle.

Answer 19

you have a right-angled triangle so you dont need to use the sine or cosine rules

Answer 20

What? So this is just as simple as Sin 45/2?

Answer 21

no - i'm assuming you want to find the sine of angle A: