20) log8 log4 log2 16 = log8 log4 4 = log8 1 = 0
21) log2 2/3 + log4 9/4 = log4 4/9 + log4 9/4 = log4 1 = 0
22) log0,5 32 - log7 √7/49 = -5 - log49 7/7⁴ = -5 - log7² 1/7³ = -5 + 3/2 =
- 3,5
23) √(25^log5 6 + 49^log7 8) = √(5^2log5 6 + 7^2log7 8) = √(5^log5 36 + 7^log7 64) = √(36+64) = √100 = 10
24) 2^log2 5 + log2 1/8 = 5 - 3 = 2
25) log4 128 = 7/2 = 3,5
26) log6 36 - log6 a = 2+6 = 8
27) logc 16 + logc c² = 4logc 2 + 2 = -12 + 2 = -10
28) loga 81 - loga a4 = 4loga 3 - 4 = 8 - 4 = 4
29) (0,1)^(-1) - 10^log10 4 + 10*100^(lg3-lg2) = 10 - 4 + 10*10^(lg9-lg4) = 10 - 4 + 10*10^lg9 / 10^lg4 = 10 - 4 + 10*9/4 = 6 + 22,5 = 28,5