t ) =  2  Sin πx    COS  100π t       x and y are in meters  and t is in seconds.we use the formula in trigonometry  2 Sin A Cos B = Sin (A+B)  + Sin (A-B)  y (x, t)  =  2  Sin (π x)     Cos (100 π t)                 =  Sin (πx + 100πt)    +    Sin  (πx - 100 πt)                 =  Sin (πx + 100πt)    -    Sin  (100πt  -  πx )                 =  Sin (100 πt + πx)   +  Sin  (100 πt  -  πx + π)general formula  for a standing wave :  y (x, t) = A Sin (ω t - k x + Ф)  these are the component WAVES which are part of the stationary wave.component wave 1:    y1 (x,t)  =  sin (π  x  +  100 π t)       angular frequency = ω    = 100 π  RADIANS/sec      frequency = f  = 50 Hz = ω/2π              TIME period: 1/f = 0.02 Sec.       Amplitude = A = 1 m       wave number  k =  - π  rad/meter                       we have formula   ω = k v           velocity  v =  ω / k  = - 100 meters/sec          wavelength λ =  v / f  =  100/50  meters =  2 meters  this component of the wave is traveling in the negative x direction. so its velocity is negative. ==========================component wave 2:    y1 (x,t)  =  sin ( 100 π t - π x +  π )       angular frequency = ω    = 100 π  radians/sec      frequency = f  = 50 Hz = ω/2π              Time period: 1/f = 0.02 Sec.       Amplitude = A = 1 m       wave number  k =  π  rad/meter                       we have formula   ω = k v           velocity  v =  ω / k  = 100 meters/sec          wavelength λ =  v / f  =  100/50   meters =  2 meters   initial phase angle = π radians this wave is traveling in the positive x direction.  so  k and v are positive.But the waves are have a phase difference also.