²log3 = a , ²log5 = b dan ²log7 = C . Berapa nilai ²log4,2 ?

²log 4,2 = ²log42/10
²log42 - ²log10
²log 3.2.7 - ²log2.5
²log3 + ²log2 + ²log7 - (²log2 + ²log5)
= a + 1 + c - 1 - b
= a+c-b