Find at least three nonzero terms (including a 0 and at least two cosine terms and two sine terms if they are not all zero) of the fourier series for the given function, and sketch at least three periods of the function. f left parenthesis x right parenthesis equals left brace start 2 by 2 matrix 1st row 1st column 7 2nd column negative pi less than or equals x less than 0 2nd row 1st column 0 2nd column 0 less than or equals x less than pi endmatrix