3log2=p, 3log5=a 3log12,5=

³log 2 = p
³log 5 = a

³log 12,5 = ³log 25/2 = ³log 25 - ³log 2
= ³log 5² - ³log 2
= 2. ³log 5 - ³log 2
= 2a – p