# Trigonometry

posted by .

I can't remember what formula to use for these.

Note- the X's may be replaced by a theta symbol. I just didn't have one on my keyboard.
Use the given information to find sin2X, cos2X and tan2X if 0< X <pi/2

1. sinX=12/13

2. cosX=3/5

3. tanX=2/3

• Trigonometry -

You use the double angle formulas.

• Trigonometry -

To type θ, you need to type the following without the double quotes nor the spaces: "& t h e t a ;".

As Diana suggested, use the double angle formulas. I'll do the first one as an example.
sin(2θ)
=2sin(θ)cos(θ)
sin(&theta)=12/13
cos(&theta)=sqrt(1²-(12/13)²)=5/13
Therefore
sin(2θ)
=2sin(θ)cos(θ)
=2(12/13)(5/13)
=120/169

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