(2/5) ^ 7x-3 = (5/2) ^ 4x+1
(5/2^-1)^7x-3=(5/2)^4x+1; (5/2)^3-7x=(5/2)^4x+1; 3-7x=4x+1; -7x-4x=1-3; -11x= -2; x=(-2)/(-11)=2/11. Ответ: x=2/11.