Question

Prove that

Answer 1

\[\cos ( 9) + \sin (9) = \sqrt{2} \sin 54\]

Answer 2

@arabpride

Answer 3

trig.?? calc.?? im no g00d at either :/ sorry .-. wish i cud help *^.^*

Answer 4

@Kainui

Answer 5

I won't ever help you unless I see you try to figure it out first.

Answer 6

How to find cos 9 @Kainui

Answer 7

I don't know how to do this

Answer 8

That's fine, that's what learning is about. You don't know something. So now it's your job to look at what you do know and see if you can try to use that to solve your problem.

I suggest you look at a table of trigonometric identities to help you out. If you don't already have one, here's a random one I found on the internet. If you search, I'm sure you can find one that you like. http://www.purplemath.com/modules/idents.htm

Answer 9

But How to find cos 9 ?

Answer 10

you may use : 45+9 = 54

Answer 11

Both angles are between 0 and 90, so that means both sides are positive.

Answer 12

in other words \(\cos(9)+\sin(9)=\sqrt{[\cos(9)+\sin(9)]^2} = \sqrt{2\sin(9)\cos(9)} \) Just throwing it out there, it may or may not help a bit.

Answer 13

@goformit100 The only reason I'm doing this is because I've noticed your past 3 questions have been of a similar nature and I think you need to show more effort in solving these. To simply say you don't know how to find something isn't good enough. It's ok to be wrong, but you can't learn without doing, otherwise when someone tells you an answer it will work but mean nothing to you.

Answer 14

Ok I am Logging off

Answer 15

ganeshie8's hint is a good one, you should definitely use it, it can lead you to the right answer. Good luck.