1. ## solve trigonometry equation

solve the equation

2cos(squared)theta=1

for 0(less than or equal to)theta(less than or equal to)2pie

(4) marks

2. Title: O dearrrrrrrrrrrrrrrrrrrrrrrrr!!!!!!!!!!!!!!
Originally Posted by eftheking
solve the equation

2cos(squared)theta=1

for 0(less than or equal to)theta(less than or equal to)2pie

(4) marks
$\displaystyle \Rightarrow \cos \theta = \pm \frac{1}{\sqrt{2}}$.

There are now two simple equations to solve. Do so.

And please refrain from the melodramatic titles.

3. apologies.yes but that then gives me 0.9etc, and how do i plot that on the CAST diagrams.
cos(-1)1/root2=0.9

4. Originally Posted by eftheking
apologies.yes but that then gives me 0.9etc, and how do i plot that on the CAST diagrams.
cos(-1)1/root2=0.9
This is wrong on three counts:

1. It's a decimal approximation to an exact value. Go back and look over your notes relating to exact values of cos for special angles ......

2. It's the wrong decimal approximation to the exact value.

3. Cosine is also positive in the fourth quadrant, so you're only considering half of the solutions to $\displaystyle \cos \theta = \frac{1}{\sqrt{2}}$.

5. wat is the key angle however

6. Originally Posted by eftheking
wat is the key angle however
Did you do as suggested in my previous post and look over your notes relating to exact values of cos for special angles? (Don't answer - I already know the answer).

$\displaystyle \frac{\pi}{4}$.