1. ## Radians. how to solve problem.

1) Give the exact value of the following: 4cos(π/4)

2) Evaluate the following expression when x is π/4. Use the exact value:

5cos(2x)

3) For the following expression, find the value of y that corresponds to each value of x, then write your results as ordered pairs (x, y). (Enter your answers from smallest to largest x-value.)

y=1/4cos(x)

x=0, π/2, π, 3π/2, 2π

thxs!

2. Originally Posted by Nismo
1) Give the exact value of the following: 4cos(π/4)

the following expression when x is π/4. Use the exact value:
$\displaystyle \cos\left(\frac{\pi}{4}\right) = \frac{1}{\sqrt{2}}$

You should memorise this value

therefore $\displaystyle 4\cos\left(\frac{\pi}{4}\right) = 4\times \frac{1}{\sqrt{2}}\dots$

Originally Posted by Nismo
2) Evaluate the following expression when x is π/4. Use the exact value:

5cos(2x)

$\displaystyle 5\cos(2x)$

$\displaystyle x=\frac{\pi}{4}$

$\displaystyle 5\cos(2\frac{\pi}{4})$

$\displaystyle 5\cos(\frac{\pi}{2})$

You should be able to finish it from here

Originally Posted by Nismo

3) For the following expression, find the value of y that corresponds to each value of x, then write your results as ordered pairs (x, y). (Enter your answers from smallest to largest x-value.)

y=1/4cos(x)

x=0, π/2, π, 3π/2, 2π

thxs!
Insert the values for x one at a time into y, here's the first one.

$\displaystyle y=\frac{1}{4}\cos(x)$

$\displaystyle x = 0$

$\displaystyle y=\frac{1}{4}\cos(0)$

$\displaystyle y=\frac{1}{4}\times 1$

$\displaystyle y=\frac{1}{4}$

3. for 1) thats as far as i got then i stopped cause i didnt know how im suspose to cross mutiple the 4 and root2 *edit nvm im so sleep deproved right now i got the answer now....*

as for 2) its the same thing i got that far and then i got stuck because how do i find a cos of pi/2 is pi/2 is the 90 degree angle?

4. Originally Posted by Nismo
is pi/2 is the 90 degree angle?
Yep

$\displaystyle \pi = 180 \Rightarrow \frac{\pi}{2} = 90$