If f and g are arbitrary functions of their respective arguments, show that u=f(x-vt+iay)+g(x-vt+iay) is a solution of d2u/dx2+d2u/dy2=1/c^2 .d2u/dt2,where a^2=1-(v^2/c^2)
If y1 = 2x + 2and y2 = −x^2/2 are the solutions of the equation y = x y′+(y')^2/ 2then are the constant multiples c1y1and c2y2 , where c1, c2 are arbitrary, also the solutions of the given de? is the sum y1+ y2 a solution? Justify your answer.