3- (Problem set 12.7) using u( x, t) = u(x, t; p) dp = [A(p) cos px + B(p) sin px] e-c-pit dp 0 Obtain the solution of au = c2 0zu ax2 in the integral form satisfying the initial condition u(x,0)=f(X), where: a. f(x)=1 if |x|