Răspuns:
Explicație pas cu pas:
1. a = log₁₂3 ; b = log₁₂5
( 1 - a + b ) / a + b
( 1 - log₁₂3 + log₁₂5 ) / log₁₂3 + log₁₂5
( log₁₂12 - log₁₂3 + log₁₂5 ) / log₁₂( 3 × 5 )
[ log₁₂( 12 × 5 ) / 3 ] / log₁₂15
[ log₁₂60 / 3 ] / log₁₂15
[ log₁₂20 ] / log₁₂15
log₁₅20 = log₁₅20 ( A ).