For a medal? Please help:if sin x=4/5 and is in quadrant 2, then tan (2x)=?

Question

mathstudent55 · Answer

Can you draw this as a graph?

anonymous · Answer

Using arcsin, right? But, is that correct when it says sin x=4/5 must have an answer in the second quadrant? Because arcsin 4/5 comes out as .927... which is not in the second quadrant in the unit circle?

anonymous · Answer

@mathstudent55

mathstudent55 · Answer

No.
It's easier than that.
Just draw an x-y coordinate plane.
Then write a terminal side of an angle in quadrant 2, so that the sine of that angle is 4/5.

mathstudent55 · Answer

|dw:1410727472447:dw|

mathstudent55 · Answer

Now you need a terminal side in Quadrant 2.

mathstudent55 · Answer

Do you follow so far?
|dw:1410727666834:dw|

anonymous · Answer

I think I get what you're saying is easier?|dw:1410727575573:dw|
Using that point to create an implied right triangle with an angle of sine? Then using that to find what tan would be? Is that in the right direction?