# Equation of a sinsuoidal graph.

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• Nov 24th 2011, 09:02 AM
crashed
Equation of a sinsuoidal graph.
Which equation is correct for this sinusoid?

And why?

http://img832.imageshack.us/img832/3400/dsc01912uz.jpg
• Nov 24th 2011, 01:16 PM
Quacky
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.
• Nov 24th 2011, 01:28 PM
TKHunny
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.
• Nov 24th 2011, 01:45 PM
mr fantastic
Re: Equation of a sinsuoidal graph.
Quote:

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

And why?

http://img832.imageshack.us/img832/3400/dsc01912uz.jpg

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.
• Nov 24th 2011, 01:51 PM
takatok
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.