((((81 x)1/3+ x)1/3+ x)1/3+ x)1/3=1

((((81 х)1/3 +х)1/3 + х)1/3 + х)1/3 = 1(((27х + х)1/3 +х)1/3 +х)1/3 =1(((28х)1/3 +х)1/3 +х)1/3 =1((28/3 * х + х)1/3 +х)1/3 =1(31/3 *х *1/3 + х)1/3 =1(31/9 *х + х) 1/3 = 140/9 *х  * 1/3 = 140 /27 *х = 140х = 27 х = 40/27