# Thread: Equation of a sinsuoidal graph.

1. ## Equation of a sinsuoidal graph.

Which equation is correct for this sinusoid?

And why?

2. ## Re: Task 1

The question doesn't really make sense. For example, take A.

We have:

$\displaystyle 2\sin{x}-1=0$

$\displaystyle 2\sin{x}=1$

$\displaystyle \sin{x}=\frac{1}{2}$

Which is solvable for $\displaystyle x$, and doesn't really represent any of the graphs.

However, you can work out which of those possible graphs could give these solutions - just solve each equation in turn for x and see which one gives the required intercepts.

3. ## Re: Task 1

Very bad choices. What's the amplitude of y = 2*cos(x) of y = 2*sin(x)?

It appears we have y = sin(x), without any alteration.

Perhaps the snie wave shown above is for reference only and this is really a four-part question. You must build the others!

Just guessing.

4. ## Re: Equation of a sinsuoidal graph.

Originally Posted by crashed
Which equation is correct for this sinusoid?

And why?

It would help if you posted the actual question exactly as written in the textbook. From the multiple choice options, I can guess that the actual question was something like "Which of the following equations gives the x-coordinates of the intersection points shown" or something similar.

You have y = sin(x) and y = 0.5. Now use what you know about solving simultaneous equations. If you need more help, please show all the effort you have made.

5. ## Re: Task 1

This question doesn't make sense for 2 reasons:
A) I'm 99.9% positive that graph is for y=sin(x). For this equation y=1/2 at 30 and 150 degrees. $\displaystyle \frac{\pi}{6}$ and $\displaystyle \frac{5\pi}{6}$ Which seems about right. However, its hard to tell the amplitude without y being labeled other than at 0.5

B) if you give a specific value like: 2sin(x)-1 = 0. You won't get a continuous graph. You will get a set of 2 points. Specifically for this one at :
$\displaystyle (\frac{\pi}{6},0)$ and $\displaystyle (\frac{5\pi}{6},0)$
This will be true of all 4 equations.