14. Determinați numărul natural x, ştiind că: a) [(2/5) ^ x] ^ 2 * (2/5) ^ 3 = (2 ^ 7)/(5 ^ 7) b) [(9/8) ^ 2] ^ 2 / ((9/8) ^ 2) =( 9 8 )^ 18 *( 9 8 )^ 2 : c) [( 4 10 )^ 2 ]^ * = (6/15) ^ (x + 13) ; (1/9) ^ 5 * (1/9) ^ 2 = (2/18) ^ 10 d) 57 * (2/10) ^ 7 = (13/11) ^ x * (11/39) ^ x​