Question

高一数学的log及其有关公式

Answer 1

loga＋logb＝logab loga÷b＝loga－logb

Answer 2

http://jingyan.baidu.com/article/e4d08ffdc1f55b0fd2f60d2e.html

Answer 3

【非原创】
本性质： 1.a^(log(a)(b))=b 2.log(a)(MN)=log(a)(M)+log(a)(N); 3.log(a)(M/N)=log(a)(M)-log(a)(N); 4.log(a)(M^n)=nlog(a)(M) 推导 1.这个就不用推了吧，直接由定义式可得(把定义式中的[n=log(a)(b)]带入a^n=b) 2. MN=M*N 由基本性质1(换掉M和N) a^[log(a)(MN)] = a^[log(a)(M)] * a^[log(a)(N)] 由指数的性质 a^[log(a)(MN)] = a^{[log(a)(M)] + [log(a)(N)]} 又因为指数函数是单调函数，所以 log(a)(MN) = log(a)(M) + log(a)(N) 3.与2类似处理 MN=M/N 由基本性质1(换掉M和N) a^[log(a)(M/N)] = a^[log(a)(M)] / a^[log(a)(N)] 由指数的性质 a^[log(a)(M/N)] = a^{[log(a)(M)] - [log(a)(N)]} 又因为指数函数是单调函数，所以 log(a)(M/N) = log(a)(M) - log(a)(N) 4.与2类似处理 M^n=M^n 由基本性质1(换掉M) a^[log(a)(M^n)] = {a^[log(a)(M)]}^n 由指数的性质 a^[log(a)(M^n)] = a^{[log(a)(M)]*n} 又因为指数函数是单调函数，所以 log(a)(M^n)=nlog(a)(M) 其他性质： 性质一：换底公式 log(a)(N)=log(b)(N) / log(b)(a) 推导如下 N = a^[log(a)(N)] a = b^[log(b)(a)] 综合两式可得 N = {b^[log(b)(a)]}^[log(a)(N)] = b^{[log(a)(N)]*[log(b)(a)]} 又因为N=b^[log(b)(N)] 所以 b^[log(b)(N)] = b^{[log(a)(N)]*[log(b)(a)]} 所以 log(b)(N) = [log(a)(N)]*[log(b)(a)] {这步不明白或有疑问看上面的} 所以log(a)(N)=log(b)(N) / log(b)(a) 性质二：（不知道什么名字） log(a^n)(b^m)=m/n*[log(a)(b)] 推导如下 由换底公式[lnx是log(e)(x),e称作自然对数的底] log(a^n)(b^m)=ln(a^n) / ln(b^n) 由基本性质4可得 log(a^n)(b^m) = [n*ln(a)] / [m*ln(b)] = (m/n)*{[ln(a)] / [ln(b)]} 再由换底公式 log(a^n)(b^m)=m/n*[log(a)(b)] --------------------------------------------（性质及推导 完 ）公式三:log(a)(b)=1/log(b)(a)证明如下:由换底公式 log(a)(b)=log(b)(b)/log(b)(a) ----取以b为底的对数,log(b)(b)=1 =1/log(b)(a)还可变形得: log(a)(b)*log(b)(a)=1