Express the waveform as a linear combination

Question

Solve the following problem:

Consider the three waveforms fn(t) shown in Figure .

a. Show that these waveforms are orthonormal.

b. Express the waveform x(t) as a linear combination of f_n(t), n = 1, 2, 3, if

            {-1   0≤t<1
 x(t)=    { 1   1≤t<3        
            {-1   3≤t<4

and determine the weighting coefficients.