2 periodic signals x(t) and y(t)of period T(0)are said to be orthogonal, if the integral over period T(0)is:
integral x(t)y(t) dt = 0
Consider x(t) = cos (pi(t)) and y(t) = sin (pi(t)). Check for repeat every T(0) = 2. Show x(t + 2) = x(t) and y(t +2) = y(t). Then use the representation of cosine in terms of complex exponential cos(thetat) = e^j theta + e ^ -jtheta / 2; to express the intergrand in terms of exponential and calculate the integral