Quadrant

[Norwegian math]

Hello. I have a question. If cos "a"=4/5 and "a" is in the first quadrant. What is the sin "a", 2cos "a" and 2sin "a"?

"a" is alfa, didnt know how to get the symbol

Thank you for help

 

[Dr.Peterson]

Hello. I have a question. If cos "a"=4/5 and "a" is in the first quadrant. What is the sin "a", 2cos "a" and 2sin "a"?

"a" is alfa, didnt know how to get the symbol

Thank you for help

It doesn't really matter what you call the angle; a is fine. To enter alpha here, you can either paste it from somewhere else, or use "\alpha" and use the calculator icon on the tool bar to enclose it.

In order to help you, though, I need to know what you have learned. You might make a right triangle and consider ratios of sides; or use identities, or several other things. Please show us an attempt, which will give us some idea of what you know.

But [MATH]2\cos\alpha[/MATH] just means 2 times the cosine, which you are given, so that is very easy. I wonder if you meant something else. You may find it useful to insert a picture of the problem.

 

[BraveHeart258]

Next time... maybe I will do an example process (If this is not deleted):

 

[Dr.Peterson]

Next time... maybe I will do an example process (If this is not deleted):

Most likely the question is asking for an exact value, obtained by means of the Pythagorean identity or an equivalent method, not inverse functions and a calculator. But we can't be sure if the OP doesn't respond, and state the entire problem.

 

[Norwegian math]

Thank you braveheart258 think you got it