If x is an acute angle and cosx=4/5, find the values of sin2x, sin3x, tan3x.

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- Dec 30th 2008, 07:19 PMmath123456trigonometry question 2
If x is an acute angle and cosx=4/5, find the values of sin2x, sin3x, tan3x.

- Dec 30th 2008, 07:23 PMnzmathman
If , then (acute angle).

Simply substitute this x value into the other equations:

?

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? - Dec 30th 2008, 08:45 PMbadgerigar
If you need an exact answer, you can use the definition of cos using a triangle.

Attachment 9418

Pythagoras' theorem can help you find sin(x). Then you can find sin(2x) and cos(2x) using the double angle formulas and then use sin(3x) = sin(x+2x) and cos(3x) = cos(2x+x) - Jan 1st 2009, 09:03 PMMush
- Jan 1st 2009, 09:05 PM11rdc11