The functions f_1, f_2, ..., f_m defined on the interval I are said to be linearly dependent on I if at least one of them can be expressed as a linear combination of the others on I. Equivalently, they are linearly dependent on I if there exist constants c_1, c_2, ..., c_m, not all zero, such that c_1 f_1 (x) + c_2 f_2 (x) + middot middot middot + c_m f_m (x) = 0 for all x I. Otherwise, they are said to be linearly independent on I. Show that the functions f_1 (x) = e^x f_2 (x) = e^-2x f_3 (x) = 3e^x - 2e^-2x are linearly dependent on (-infinity, infinity). Solution Given that f1(x) = ex , f2(x) = e-2x and f3(x) = 3ex - 2e-2x Then there exists non-zero constants C1 = - 3 , C2 = 2 and C3 = 1 such that C1f1(x) + C2 f2(x) + C1f3(x) = 0. Hence The functions f1( x) = ex , f2(x) = e-2x and f3(x) = 3ex - 2e-2x are linearly dependent for all x *( - , ).