1. ## Trigonometry

find exact value

cos30 cos60 - sin30 sin60

0

3. ## Re: Trigonometry

You sure are asking a lot of exact value questions!

$\frac{\sqrt 3}{2} \times \frac{1}{2} - \frac{1}{2} \times \frac{\sqrt 3}{2} = 0$

Another way of doing this is recognising the Compound Angle formula for cos(a+b), which gives us cos(30+60)=cos(90), which is equal to 0.

4. ## Re: Trigonometry

Originally Posted by Fus Ro Dah
You sure are asking a lot of exact value questions!

$\frac{\sqrt 3}{2} \times \frac{1}{2} - \frac{1}{2} \times \frac{\sqrt 3}{2} = 0$

Another way of doing this is recognising the Compound Angle formula for cos(a+b), which gives us cos(30+60)=cos(90), which is equal to 0.
Compound angles are a 3u topic, though.

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