# Prove 1+1=2 using trigonometric functions

1. Jun 7, 2009

### jontyjashan

Prove
1+1=2
using trigonometric functions

2. Jun 7, 2009

### dx

Re: 1+1=2

That makes no sense. Why on earth would you think that trigonometric functions are involved in the proof of 1 + 1 = 2?

3. Jun 7, 2009

### Cyosis

Re: 1+1=2

Bit of an odd requirement, but I guess if you're allowed to use trig identities you can do it. The problem is though can we derive those identities without using simple addition in the first place, therefore do it without circular reasoning.

What is the purpose of this exercise, are you studying trigonometric identities? If this is an exercise to test your knowledge of trigonometry you could for example use:
$$\cos x +\cos y=2\cos((x+y)/2)\cos((x-y)/2)$$

Last edited: Jun 7, 2009
4. Jun 7, 2009

### mma

Re: 1+1=2

This proves 1 + 1 = 1
:-)

5. Jun 7, 2009

### sylas

Re: 1+1=2

... for a sufficiently large value of 1.

6. Jun 7, 2009

### Cyosis

Re: 1+1=2

Whoops, lets be glad the formula I listed is wrong or we would be in trouble!

I forgot a factor of two it should of course be.

$$\cos x +\cos y=2\cos((x+y)/2)\cos((x-y)/2)$$

Fixed it in the original post as well.

7. Jun 7, 2009

### jontyjashan

Re: 1+1=2

how this proves 1+1=2
give detail

8. Jun 7, 2009

### Dragonfall

Re: 1+1=2

You don't prove 1+1=2 using trigonometric functions. You do that in set theory, or math logic.

9. Jun 8, 2009

### boboYO

Re: 1+1=2

troll

10. Jun 8, 2009

### mma

Re: 1+1=2

Substitute x = y = 0.

11. Jun 8, 2009

### Cyosis

Re: 1+1=2

I am kind of starting to suspect this he is a troll as well. If you look at all his other topics, every post is vague, borderline preposterous and when asked to clarify he never bothers to do so.

12. Jun 8, 2009

### jontyjashan

Re: 1+1=2

i m not a troll

13. Jun 8, 2009

### Cyosis

Re: 1+1=2

Then could you explain the reason behind this question perhaps? I have a hard time believing this is a text book problem.

14. Jun 8, 2009

### jontyjashan

Re: 1+1=2

this is not a textbook question

15. Jun 9, 2009

### HallsofIvy

Staff Emeritus
Re: 1+1=2

Then what kind of question is it? Why are you insisting that a proof of such a fundamental property (it really is, basically, the definition of "2") use such sophisticated tools as trig functions?