Cosine

[RHONDAROBINSON]

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Please help with problem.

The value of cos(pi/3) equals the value of:

a. -cos (2pi/3)
b. cos (2pi/3)
c. cos (6pi/3)


Rhonda

 

[TKDentist]

you could just use a calculator, but its A.

 

[Ibraiz]

Calculator on DAT computer, does it have sin cos on them that we can use?

 

[299678]

answer is a?
cos pie/3 = cos 120 by using reference angle (180-pie), since cos 120 is located on second quadrant, which give u negative.

 

[RHONDAROBINSON]

So, would cos(pi/4) equal -cos 3pi/4 at 135 degrees?

Rhonda

 

[TKDentist]

Calculator on DAT computer, does it have sin cos on them that we can use?

I would think so, but I could be wrong.

 

[herkulease]

I would think so, but I could be wrong.

The calculator is extremely basic. Just run the calculator on windows and select the basic one. That's what you get.

So, would cos(pi/4) equal -cos 3pi/4 at 135 degrees?

Rhonda

Yup.

Determine your angle unless they give it to you. Then use the mneumonic All Students Take Calculus(or some variation of it) to know where certain values have to be positive or negative.

Then determine your reference angle.

If its in quad 1, the angle given is your reference angle.
If its in quad 2, 180 - angle = reference angle
If its in quad 3, Angle - 180 = reference angle
If its in quad 4, 360 - angle = reference angle

 

[RHONDAROBINSON]

Thanks everyone. This was one of the questions on the practice DAT from ADA. The correct answer is A.


Rhonda

 

[Frederico Albin]

answer is a?
cos pie/3 = cos 120 by using reference angle (180-pie), since cos 120 is located on second quadrant, which give u negative.

?????? did i misread your msg or something?
cos pie/3 is not equal to cos 120...

pie/3 x 180/pie = 60 degrees.

cos pie/3 = cos 60

Edit. oh, maybe you tried to say "cos 2pie/3 = cos 120" 🙂

 

[Frederico Albin]

Since trig comes easily to me, here is a little more explanation 🙂