Math Is Fun Forum

zee-f

Member

Registered: 2011-05-12

Posts: 1,220

Trigonometry

Hi guys,

I know how to find the sine, cosine, and tangent but this problem is confusing any clues ? I just what to know how to get the adjacent, hypotenuse,and opposite.

Still looking at the image above, one angle is angle x, and another is the right angle (90o). Since the angles in a triangle add up to 180o, the other angle will be 90-x. For the unlabeled angle above, the angle 90-x:

7. What is the sin?
A 0.3
B 0.6
C 0.9
D0.4
E 0.2
F 0.5

8. What is the cos?

A 0.8
B0.2
C0.6
D0.4
E 0.1
F 0.9

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One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

zee-f

Member

Registered: 2011-05-12

Posts: 1,220

Re: Trigonometry

This is the image they talk about do I still use the same numbers?

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One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

zee-f

Member

Registered: 2011-05-12

Posts: 1,220

Re: Trigonometry

ooooooooh I get it I still use the same numbers but the angle is different Never mind guys it's clear now so the answers would be :
7. b
8. a

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One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

Calligar

Member

Registered: 2011-09-24

Posts: 272

Re: Trigonometry

Well, I would assume you would have to use the image, as I see no other way of getting the answer unless I am mistaken.  Both 7. and 8. seem to be answers you must choose from that I would otherwise think only have one correct answer.  However, from my personal results, I see a problem in this...particularly 7. doesn't seem to fit any of the selected answers making me think I'm either doing something wrong (like I have sin and cos confused), or you are only supposed to select the closest answer.  Let me explain what I did...

I only used the image for this, as I don't currently see another way of doing this at the moment.
7.  I took the number 4 (the opposite) and divided it by the number 5 (the hypotenuse), and got 0.8, thus that SHOULD be the sine, but if you see, there is no answer for that, the closest one would be C 0.9...
8.  I took the number 3 (the adjacent) and divided it by the number 5 (the hypotenuse), and got 0.6, which should be the cos.  If that is correct, it would be C 0.6

Now, because 7. does not equal the correct answer, I would personally wait for someone else to either verify or correct this.  I'm sorry ahead of time is this is not correct.

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There are always other variables.  -[unknown]
But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end.  -Aristotle
Everything makes sense, one only needs to figure out how.  -[unknown]

Calligar

Member

Registered: 2011-09-24

Posts: 272

Re: Trigonometry

Sorry posted too late, if you are correct though, then it seems I did have sin and cos backwards, thanks...

But I would like to know why 4 is the adjacent and not the opposite, same goes for 3 but visa versa...

Last edited by Calligar (2012-10-11 12:36:38)

---

There are always other variables.  -[unknown]
But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end.  -Aristotle
Everything makes sense, one only needs to figure out how.  -[unknown]

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Trigonometry

hi zee-f,

If the diagram in post 2 is the correct one to use then:

the longest side is the hypotenuse and that is 5

the adjacent is next to the x and that is 3

the side opposite the x is 4

so sin x is O/H = 4/5 = 0.8

and cos x = A/H = 3/5 = 0.6

If you are being asked for sin( 90 -x) then the adjacent and opposite for that angle are the other way round so

sin(90-x) = 0.6
cos(90-x) = 0.8

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Calligar

Member

Registered: 2011-09-24

Posts: 272

Re: Trigonometry

Okay, so sorry, maybe it is your wording, but I am a little bit confused.  Your saying the answer for both sine and cosine was 90 degrees - x?  I'm probably misunderstanding the problem, but I really don't understand why that is.  Would it be possible to explain further?

---

There are always other variables.  -[unknown]
But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end.  -Aristotle
Everything makes sense, one only needs to figure out how.  -[unknown]

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Trigonometry

I am making an assumption that one diagram is used for several questions and that for this question

For the unlabeled angle above, the angle 90-x:

So the question wanted sin/cos(90-x) not sin/cos x

the alternative answers offered would suggest this is a correct assumption.

I am not surprised that you also have found this confusing.  In the past I have often been confused by the worksheets on the course zee-f is doing.

Sometimes it has taken us longer to sort out what the question means than get the answer.

Have a look at post 90 on

http://www.mathisfunforum.com/viewtopic … =15902&p=2

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Calligar

Member

Registered: 2011-09-24

Posts: 272

Re: Trigonometry

Note taken, thanks...

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There are always other variables.  -[unknown]
But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end.  -Aristotle
Everything makes sense, one only needs to figure out how.  -[unknown]