同底的對數(shù)相加,結(jié)果等于真數(shù)積的對數(shù)
真數(shù)之積為
cosπ/9cos2π/9cos4π/9
=(8sinπ/9cosπ/9cos2π/9cos4π/9)/(8sinπ/9)
=4sin2π/9cos2π/9cos4π/9)/(8sinπ/9)
=(2sin4π/9cos4π/9)/(8sinπ/9)
=(sin8π/9)/(8sinπ/9)
=(sin(π-π/9))/(8sinπ/9)
=1/8
所以log2 (1/8)=-3,即原式=-3
求log以2為底cosπ/9的對數(shù)+log以2為底cos2π/9+log以2為底4π/9=
求log以2為底cosπ/9的對數(shù)+log以2為底cos2π/9+log以2為底4π/9=
數(shù)學(xué)人氣：547 ℃時間：2020-05-21 07:33:19
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