A right isosceles triangular membrane with leg length 
, whose boundary is a right
isosceles triangle with legs oriented along the positive 
and 
axes, has equation of motion
![psi(x,y,t)=[C_(pq)cos(omega_(pq)t)+D_(pq)sin(omega_(pq)t)][sin((ppix)/c)sin((qpiy)/c)-sin((qpix)/c)sin((ppiy)/c)],](/images/equations/RightIsoscelesTriangularMembrane/NumberedEquation1.svg) |
where
 |
and 
, 
integers with 
. This solution can be obtained by subtracting
two wave solutions for a square membrane with the indices reversed. Since points
on the diagonal which are equidistant from the center must have the same wave equation
solution (by symmetry), this procedure gives a wavefunction which will vanish along
the diagonal as long as 
and 
are both even
or odd. We must further restrict
the modes since those with 
give wavefunctions which are just the negative
of 
and 
give an identically zero wavefunction.
The plots above show the lowest order spatial modes.
