A standing wave pattern on a string is described by
y(x,t)=0.030sin(7πx)cos(40πt).
Determine the location of the first three nodes for 0≤ x ≤ 0.36m.

My attempt: k= 2pi/lambda k=(7pi)
so wavelength(lambda) = 2pi/k . I solved for wavelength = 2/7m .
Then solved to find the nodes, since nodes are found a 0,lambda/2,lambda, and 3lambda/2. To find 0m ,1/7m and 2/7m. But it tells me i'm wrong for some reason.

Question

A standing wave pattern on a string is described by 
y(x,t)=0.030sin(7πx)cos(40πt).
Determine the location of the first three nodes for 0≤ x ≤ 0.36m.

My attempt: k= 2pi/lambda  k=(7pi) 
so wavelength(lambda) = 2pi/k . I solved for wavelength = 2/7m . 
Then solved to find the nodes, since nodes are found a 0,lambda/2,lambda, and 3lambda/2. To find 0m ,1/7m and 2/7m. But it tells me i'm wrong for some reason.