# Trig - Quadratic Function Help

• Apr 22nd 2009, 12:21 PM
Maccabhoy
Hi, first time poster, long time reader, Here I am as im stuck on some questions for a quiz. Ive looked in notes and books and still cant figure them out...anyway, here they are. Can anyone give me a clue, how I do it...or even the answers...aha..preferably both!

What angles (in radians) in have a cosine of

1 /2

I know the answer to this is pi/3.

The next question is:

In which quadrant is the other angle whose cosine is

1 / 2

And I know it is Quad 4...

Now...what I dont know is Part C) which is....

So how do I find out the angle not in the first quadrant (which is worked out to be Quad 4)?

...............

(I am also stuck on the same question where the angle is pi/6 and need the angle in the 3rd quadrant)
• Apr 22nd 2009, 12:40 PM
masters
Quote:

Originally Posted by Maccabhoy
Hi, im stuck on some questions for a quiz. Ive looked in notes and books and still cant figure them out...anyway, here they are. Can anyone give me a clue, how I do it...or even the answers...aha..preferably both!

What angles (in radians) in have a cosine of

1 /2

I know the answer to this is pi/3.

The next question is:

In which quadrant is the other angle whose cosine is

1 / 2

And I know it is Quad 4...

Now...what I dont know is Part C) which is....

So how do I find out the angle not in the first quadrant?

...............

(I am also stuck on the same question where the angle is pi/6 and need the angle in the 3rd quadrant)

Hi Maccabhoy,

In all that wording, I'm not sure what you can't find. Sounds like you need a picture of the unit circle. Look here! Print yourself a copy and keep it handy.

As you can see from the table $\cos \frac{\pi}{6}=\frac{1}{2}$ which is in QI.

And $\cos \frac{5\pi}{3}=\frac{1}{2}$ in QIV.

• Apr 22nd 2009, 12:52 PM
Maccabhoy
Quote:

Originally Posted by masters
Hi Maccabhoy,

In all that wording, I'm not sure what you can't find. Sounds like you need a picture of the unit circle. Look here! Print yourself a copy and keep it handy.

As you can see from the table $\cos \frac{\pi}{6}=\frac{1}{2}$ which is in QI.

And $\cos \frac{5\pi}{3}=\frac{1}{2}$ in QIV.

Hey Masters, thanks for the reply. Not sure you have answered the question.... But that's my fault, as I think my explanation isnt the best. I'll try to copy and paste the question direct (As you will see, I got the answers for 8.1 and 8.2 correct and just need 8.3)

----------------------

What angles (in radians) in have a cosine of
1/2?
Your angles should be given exactly. Recall that π is entered as: pi or Pi.
8.1 (1 mark)

1/3 π

The mark for your last attempt was 1.00

8.2 (1 mark)
In which quadrant is the other angle whose cosine is 1/2 ?

Note: penalties for wrong answers are higher than usual. Don't just guess!

4

The mark for your last attempt was 1.00

8.3 (1 mark) Angle not in 1st quadrant:
• Apr 22nd 2009, 12:57 PM
Maccabhoy
And here is the other question, where again ive answered 9.1 and 9.2 correctly but can't figure out 9.3

Question 9 (3 marks) Top 1 2 3 4 5 6 7 8 9 10 Bottom Validate Mark Focus Help What are the angles (in radians) whose tangent is

1 /√3
? Your angles should be given exactly. Recall that π is entered as: pi or Pi.
9.1 (1 mark)

1/6 π

The mark for your last attempt was 1.00

9.2 (1 mark)
In which quadrant is the other angle whose tangent is

1 /√3

Note: penalties for wrong answers are higher than usual. Don't just guess!

3

The mark for your last attempt was 1.00

9.3 (1 mark)

• Apr 22nd 2009, 01:00 PM
masters
Quote:

Originally Posted by Maccabhoy
Hey Masters, thanks for the reply. Not sure you have answered the question.... But that's my fault, as I think my explanation isnt the best. I'll try to copy and paste the question direct (As you will see, I got the answers for 8.1 and 8.2 correct and just need 8.3)

----------------------

What angles (in radians) in have a cosine of
1/2?
Your angles should be given exactly. Recall that π is entered as: pi or Pi.
8.1 (1 mark)

1/3 π

The mark for your last attempt was 1.00

8.2 (1 mark)
In which quadrant is the other angle whose cosine is 1/2 ?

Note: penalties for wrong answers are higher than usual. Don't just guess!

4

The mark for your last attempt was 1.00

8.3 (1 mark) Angle not in 1st quadrant:

Looks to me like they're asking for the angle in quadrant IV whose cosine is also 1/2 which would be $\frac{5\pi}{3}$. This angle is not in the 1st quadrant and seems to answer the question. Am I missing something?
• Apr 22nd 2009, 01:12 PM
Maccabhoy
Quote:

Originally Posted by masters
Looks to me like they're asking for the angle in quadrant IV whose cosine is also 1/2 which would be $\frac{5\pi}{3}$. This angle is not in the 1st quadrant and seems to answer the question. Am I missing something?

No that is right! Thanks! I had typed that previously but got it wrong as I wasnt using the correst syntax for this online program!!