(х^а)^б=х^аб
(а^(3/13)^3=а^(9/13)
4а^(9/13)-14а^(9/13)=-10а^(9/13)
12/х=3/2.
х=(12*2/3)=8.
Ответ:8.
(0.4)^(9-x^2)<=1
(0.4)^(9-x^2)<=(0.4)^0
9-x^2<=0
(x-3)(x+3)>=0
=============-3=========3===========
++++++++++++++------------------+++++++++++
(-бесконечность -3]U[3 + бесконечность)