26. Source CW oscillates according to the law x = 0,4cos60πt, m. The wave velocity υ = 90 m / s. Write the equation of a plane wave propagating along the line, which coincides with the positive direction of the x-axis in the medium does not absorb energy. Determine: 1) the length λ of the traveling wave; 2) displacement of ξ1 and ξ2 points of the medium, which are on the line at distances x1 = 20 and x2 = m 21 m from the source, at t = 2 s from the beginning of the oscillation source; 3) the phase difference Δφ oscillation points 1 and 2.