If x is an acute angle and cosx=4/5, find the values of sin2x, sin3x, tan3x.
Follow Math Help Forum on Facebook and Google+
If , then (acute angle).
Simply substitute this x value into the other equations: ? ? ?
If you need an exact answer, you can use the definition of cos using a triangle.
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)
Originally Posted by math123456 if x is an acute angle and cos x=4/5, find the exact values of sin2a, sin3a and tan3a. cos(x) = adjacent/hypotenuse.
So adjacent = 4
Hypotenuse = 5.
You can use pythagorus to work out the opposite side, and the use that to find sin(x) = opposite/hypotenuse.
Last edited by mr fantastic; Jan 1st 2009 at 08:47 PM.
Reason: No edit - just flagging this reply as having been moved from a double post
Originally Posted by math123456 if x is an acute angle and cos x=4/5, find the exact values of sin2a, sin3a and tan3a. Ok since is an acute ww can concur that sin is positive as well
Using pythagorean theorem we see that
Now just plug in and solve
View Tag Cloud