Trig Help.

Question

Trig Help.

anonymous · Answer

$$\sin(\frac{ 3\pi }{ 4})$$

anonymous · Answer

Question?

anonymous · Answer

Use the reference angle to find the exact value of each expression.

anonymous · Answer

3pi/4 is part of the pi/4 family (the reference angle is pi/4). Sine of pi/4 is 1/sqrt2. Since 3pi/4 is in the second quadrant, its sine is still positive and so sin of 3pi/4 = 1/sqrt2, or sqrt2/2.

anonymous · Answer

okay so what is sin(pi/4)?

anonymous · Answer

then, determine if it is positive or negative, depending on the quadrant, which in this case is 2

anonymous · Answer

@robz8 that is where i got stuck, cause my angle was in the second quadrant :/

anonymous · Answer

okay, so i sin positive or negative in the second quadrant?

anonymous · Answer

To write this in a cleaner way (it looks a little weird up there):
$$\sin(\frac{ \pi }{ 4 }) = \frac{ \sqrt{2} }{ 2 }$$pi/4 is a reference angle to 3pi/4
|dw:1367636452903:dw| So $$\sin (\frac{ 3\pi }{ 4 }) = \frac{ \sqrt2 }{ 2 }$$

anonymous · Answer

See, what you should really try to get is where sine is positive and negative. That way, you just have to find whatever angle you're looking for's reference angle and then decide if it's pos or neg.

anonymous · Answer

@thechocoluver445 actually the answer is $$-\frac{ \sqrt{2} }{ 2 }$$
but i did get till up to $$\frac{ \sqrt{2} }{ 2 } = \sin \frac{ 3\pi }{ 4 }$$

anonymous · Answer

@some_someone No, it's positive. I think you're thinking of cosine.

anonymous · Answer

sin is negative in the 2nd quadrant i believe

anonymous · Answer

No, that's cosine! http://www.regentsprep.org/Regents/math/algtrig/ATT5/UnitCirclePic.pdf

anonymous · Answer

@thechocoluver445 yes! i was looking at the wrong problem :/ lol thnx that is where i was confused i got positive and i thought it said the answer was negative.. thank you all :D

anonymous · Answer

Oh lol that's good to hear! :)
But if you're still a little iffy
|dw:1367636747657:dw|
|dw:1367636793885:dw|

anonymous · Answer

That is why i was confused.

anonymous · Answer

It's ok, happens to the best of us :D

anonymous · Answer

Thank you @thechocoluver445 :D

anonymous · Answer

No problem :)

anonymous · Answer

sin isn't negative until pi... if you look at the sin's graph in cartesian coordinates

anonymous · Answer

right?

anonymous · Answer

it is positive, @robz8 
@thechocoluver445 was right.

anonymous · Answer

Yep. Because after pi, you enter quadrants 3 and 4, where sine is negative

anonymous · Answer

oh wow i'm stupid, i was arguing against myself haha