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  • 1 # 南風微涼南巷茶色

    當a>0且a≠1時,m>0,n>0,那麼:

    (1)log(a)(mn)=log(a)(m)+log(a)(n);

    (2)log(a)(m/n)=log(a)(m)-log(a)(n);

    (3)log(a)(m^n)=nlog(a)(m)(n∈r)

    (4)換底公式:log(a)m=log(b)m/log(b)a(b>0且b≠1)

    (5)a^(log(b)n)=n^(log(b)a)證明:

    設a=n^x則a^(log(b)n)=(n^x)^log(b)n=n^(x·log(b)n)=n^log(b)(n^x)=n^(log(b)a)

    (6)對數恆等式:a^log(a)n=n;

    log(a)a^b=b

    (7)由冪的對數的運算性質可得(推導公式)

    1.log(a)m^(1/n)=(1/n)log(a)m,log(a)m^(-1/n)=(-1/n)log(a)m

    2.log(a)m^(m/n)=(m/n)log(a)m,log(a)m^(-m/n)=(-m/n)log(a)m

    3.log(a^n)m^n=log(a)m,log(a^n)m^m=(m/n)log(a)m

    4.log(以n次根號下的a為底)(以n次根號下的m為真數)=log(a)m,

    log(以n次根號下的a為底)(以m次根號下的m為真數)=(m/n)log(a)m

    5.log(a)b×log(b)c×log(c)a=1

    對數與指數之間的關係

    當a>0且a≠1時,a^x=nx=㏒(a)n

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