Trigonometry

**nsbrando** · 25 Jun 2012, 5:48 PM

find exact value

cos30 cos60 - sin30 sin60

**zeebobDD** · 25 Jun 2012, 5:50 PM

0

**Fus Ro Dah** · 25 Jun 2012, 5:51 PM

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.

**Shadowdude** · 25 Jun 2012, 10:25 PM

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.