A^x =b, x =log(a)b
1) 2^x =5
x =log(5) /log(2)
2) 1.2^x =4, где 1.2^x =(6/5)^x
(6/5)^x =4, x =log(4) /log(6/5)
3) 4^(2x+3) =5
2x+3 =log(5)/log(4)
2x =(log(5)/log(4)) -3
x =log(5)/2log(4) -3/2
4) 7^(1-2x) =2
7^(2x-1) =1/2
2x -1 = -log(2)/log(7)
x =1/2 -log(2)/2log(7)