# What is the x>0 mean here? standing wave equation find nodes?

1. Jun 11, 2013

### Outrageous

1. The problem statement, all variables and given/known data
Two waves travel in opposite direction form a standing wave of y= 2sin(31.42x)cos(7854t).
Find the positions of first two nodes with x>0.

2. Relevant equations

3. The attempt at a solution
The question didn't say whether the standing wave starts from node or antinode . The question didn't say how long is x, even I know the wavelength and frequency also don't know how to calculate, how? Please help

2. Jun 11, 2013

### Dick

Tell me what 'node' means.

3. Jun 12, 2013

### Outrageous

The point that is not moving in standing wave. X=0. Then t= 0 ,then I will get first node, the second node, t=2?

Thanks

4. Jun 12, 2013

### Dick

No, a node is a point where y=0 for all values of t. Try to find the first two value of x that satisfy 2sin(31.42x)=0.

5. Jun 12, 2013

### Outrageous

Yup, y=0, thank you very much

6. Jun 13, 2013

### Outrageous

Then for antinode position is dy/dT= 0 ? The amplitude is maximum for all kind of y.

7. Jun 13, 2013

### Outrageous

The position of the first two antinode s with x< 0. X<0 here mean they want the x value be negative , if I use, dy/dt = 0, then I will get sin34.42x= 0 , how to make x become less than zero here? Please thanks

8. Jun 13, 2013

### Dick

Antinode is where the amplitude reaches a maximum as a function of x. To find maxima you want to use calculus and solve dy/dx=0.

9. Jun 13, 2013

### Outrageous

Why I can't use dy/dT=0? Is that because x<0? What does that mean ? please .