Find the point on the terminal side of $\theta~=~-\dfrac{3\pi}{4}$ that has an x coordinate of -1. Show your work.

Question

sleepyjess · Answer

@Callisto

callisto · Answer

What is $\frac{3\pi}{4}$ in degrees?

sleepyjess · Answer

$\dfrac{3\pi}{4}*\dfrac{180}{\pi}=\dfrac{540\pi}{4\pi}\pi~cancels\\dfrac{540}{4}=135$

callisto · Answer

Yes. So, $-\frac{3\pi}{4} $=-135°
Can you locate where -135° is in this drawing?
|dw:1415498434453:dw|

sleepyjess · Answer

|dw:1415498491744:dw|

callisto · Answer

Mark the x-coordinate.
|dw:1415498681333:dw|
Can you find the y-coordinate?

sleepyjess · Answer

-1, -1?

callisto · Answer

Yes

sleepyjess · Answer

how would I explain how I got the y? just say that I drew the line at -135 and looked at what y is when x is -1?

callisto · Answer

Have you learnt trigonometric ratios?

sleepyjess · Answer

like sine, cosine, tangent, etc?

callisto · Answer

Yes

sleepyjess · Answer

would tan(-135)=$-\tfrac{y}{1}$ be correct?

callisto · Answer

$$\tan(-135) = \frac{y}{-1}$$

sleepyjess · Answer

tan(-135)=1
1=y/-1
*-1
-1=y

callisto · Answer

y=-1
Make sure you have the unknown on the left of the equation.