Hello,

Can someone please help me with these problems?

Find Sin2x, Cos 2x, and Tan2x for:

1. tan x= -4/3 quadrant II

2. csc x = 4, tan x<0

how do I start the problem?

for 1, is Sin -4/1 and Cos 3/1

and for 2 is sin 1/4?

Thanks

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- Nov 2nd 2009, 01:49 PMl flipboi lDouble-Angle Formulas
Hello,

Can someone please help me with these problems?

Find Sin2x, Cos 2x, and Tan2x for:

1. tan x= -4/3 quadrant II

2. csc x = 4, tan x<0

how do I start the problem?

for 1, is Sin -4/1 and Cos 3/1

and for 2 is sin 1/4?

Thanks - Nov 3rd 2009, 07:01 AMGrandad
Hello l flipboi lAre you familiar with this diagram that tells you when the various trig functions are positive?

1. In QII, only sine is positive. So if and is in QII, and (using Pythagoras). You should be able to find the sine, cosine and tangent of using the standard double-angle formulae.

2. You are right: . Since sine is positive, we are either in QI or QII. So the fact that means that must be in QII. Using Pythagoras, then:andAgain, the standard double-angle formula will give you the results you need.

Grandad - Nov 3rd 2009, 10:15 AMl flipboi l