# I have no clue what to do with Trigonometry

1. Feb 22, 2017

### Carson Steele

I have been failing some tests on trig and one question was sinx=cos48. I have no clue what it means, please help

2. Feb 22, 2017

### Janus

Staff Emeritus
It's basically asking what value of x, if you take its sin, gives you the same answer as when you take the cos of 48.

3. Feb 22, 2017

### Carson Steele

Thanks for replying but you are still taking gibberish to me

4. Feb 22, 2017

### mathman

Let a=cos48. Let sinx=a, find x. Also sinx=cos(90-x). 90-x=48, find x.

5. Feb 22, 2017

### Staff: Mentor

There are some good short video tutorials at mathispower4u.com on trigonometry.

I would suggest working through them one by one doing the problems they do as they do it.

http://www.mathispower4u.com/trigonometry.php

6. Feb 22, 2017

### symbolipoint

Studying Physics may help to make Trigonometry seem sensible. Basically, the trigonometric functions are cyclic functions, based on reference to circles and triangles. One needs to learn to make diagrams and draw and label figures.

7. Feb 23, 2017

### Demystifier

8. Feb 23, 2017

### Nidum

+1

9. Feb 23, 2017

### Logical Dog

Do you know what a set, element of a set, ordered pair? function? the definition of a functions domain, co -domain, image? functions defined as ordered pairs...variables like x y z are generic letters that stand for any element of a larger set:

https://en.wikipedia.org/wiki/Domain_of_discourse

https://en.wikipedia.org/wiki/Domain_of_a_function
https://en.wikipedia.org/wiki/Codomain
https://en.wikipedia.org/wiki/Range_(mathematics)

http://www.dummies.com/education/math/pre-algebra/evaluate-mathematical-expressions/
the whole sentence you posted there is called a mathematical expression, a mix of letters and symbols. The equal symbol is a mathematical relation, it states that two mathematical objects when evaluated, are equal.

So sin x = cos 48 means what is the number that can replace x so that the value of the sine of that number is equal to the number that is evaluated when we put cos 48.
As for what the sin, cos, tan functions you might want to read this:

https://en.wikipedia.org/wiki/Trigonometric_functions

for a basic introduction to set thoery and functions as ordered pairs and relations you can check this page:
http://www.people.vcu.edu/~rhammack/BookOfProof/

10. Feb 23, 2017

### gleem

What is the meaning of sin(x). draw a triangle with a unit length hypotenuse to represent x. What does sin(x) represent in your triangle. . Now repeat with a different triangle for another angle y. What does cos(y) represent in this triangle?

Now if sin(x) = cos(y) orient the triangles so that they are opposite one another. I there anything you can say about the relationship of x to y?

11. Feb 23, 2017

### vela

Staff Emeritus
What are you doing taking trig if you don't know basic mathematics?

12. Feb 23, 2017

### symbolipoint

Maybe the wrong understanding. Maybe Carson Steele went through Algebra 2, but many parts of Trigonometry don't make sense to him; they are too much for him but WE do not know why. MAYBE he needs to go through one or two of his earlier courses again, so that he might learn them better, and be well prepared to handle learning Trigonometry.

13. Feb 23, 2017

### gleem

The question that he had a problem with has nothing to do with algebra. He was not paying attention in class or did not read the text. It is about the relationship between two trigonometric quantities. The sine of an angle is equal to the cosine of its complement for a right triangle.

14. Feb 23, 2017

### vela

Staff Emeritus
I don't know. It seems a bit extreme to have "no clue what it means." That's quite different than simply not knowing how to solve the problem.

15. Feb 23, 2017

### Logical Dog

Op you could also read pre math and algebra for dummies, its a great book and even I go back to it from time to time. Mark Z is a great author and i like all his books on math and logic.

Mark Zegarelli - basic math and pre algebra for dummies. Its hard to help you without an understanding of your background, this unfortunately entails a general knowledge of the landscape of matheamtics.

Last edited: Feb 24, 2017
16. Feb 24, 2017

### Demystifier

You are joking, right? Or do you really think that it could help someone who thinks that a statement in post #3 is a gibberish? I wouldn't be too surprised if he even didn't know what to do with 90-x=48 in post #4.

Or maybe he should first read Principia Mathematica by Whitehead and my avatar to see the proof that 1+1=2?

Last edited: Feb 24, 2017
17. Feb 24, 2017

### symbolipoint

Look at what I said back in post #12. Maybe the member did pass Algebra 1 and Algebra 2, but things just are not working for him in his try to learn Trigonometry. The Algebras are a different subject than Trigonometry. The combination of Geometry and cyclic functions may be too much for him right now, and in fact, he MAY NEED TO THOROUGHLY RESTUDY SOMETHING FROM PREVIOUS COURSES. Has a student ever been given a grade higher than he deserved, enrolled in the next course, and done badly?

18. Feb 24, 2017

### Logical Dog

hahahahahahah xD...unfortunately I was quite serious

editL in all seriousness people need to know these things, they are basic, along with peano axioms. I guess its just up to the level where you can apply them effectively, but i want to learn it for the sake of it.

Last edited: Feb 24, 2017
19. Feb 24, 2017

### stevendaryl

Staff Emeritus
Well, if you try $x=42^o$, then you can demonstrate by using your calculator that:

$sin(42^o) = cos(48^o)$

$sin(x) = cos(48^o)$

and replace $x$ by $42^o$, then you get a true statement. That's what it means to "solve" an equation such as $sin(x) = cos(48^o)$; it means find a substitution for $x$ that makes the equation true.

20. Feb 24, 2017

### Demystifier

I also want to learn it for the sake of it, but OP just wants to pass the trigonometry exam. And obviously, his level in math is very low.

By the way, in the first year of elementary school we were taught sets before we were taught counting 1,2,...,10. It was a very modern approach to teaching mathematics at that time.

21. Feb 24, 2017

### Logical Dog

the reality is whether for self fullfilment or for achieving anything useful, one has to learn it. There is no choice especially in the field of science. I believe in this time and after, No human will ever accomplish anything useful without having used some mathematics or some object born out of the use or relying on the principles of mathematics...for the most part.

I had no choice, but luckily I loved debating and combining old information to derive new, and argument structure and logic are crucial in mathematics. So I got lucky there.

22. Feb 24, 2017

### Demystifier

Sure, even your avatar dog uses a laptop, and the laptop relies on the principles of mathematics. But it doesn't mean that the dog himself knows any mathematics. Similarly, people who (for instance) use facebook can do many useful things with it. But it doesn't mean that they must know any mathematics to use facebook, despite the fact that facebook relies on the principles of mathematics.

23. Feb 24, 2017

### Logical Dog

Yes, and that dog is me. Whats your point?
I tought i knew a little
agree but even basics like addition subtraction, multiplication division, the decimal system, should not be taken for granted.

Last edited: Feb 24, 2017
24. Feb 24, 2017

### Demystifier

A logical dog would not ask such an obvious question. This proves that your dog is more logical than you.

25. Feb 24, 2017

### Logical Dog

But we are both the same thing, dog = me. No evil xy variables in this expression!