99屏東女中

[nicklin9192]

多謝

[nicklin9192]

我的問題是不用計算機之下如何用手算15.75*(1/3)次方30,麻煩老師!

[thepiano]

令 x = 15.75 * (1/3)^30 = (63/4) * (1/3)^30

logx = log63 - log4 - 30log3
= 2log3 + log7 - 2log2 - 30log3
= log7 - 28log3 - 2log2
= 0.8451 - 28 * 0.4771 - 2 * 0.301
= - 13.1157
故 k = 14

又 -13.1157 + 14 = 0.8843
log7 ＜ 0.8843 ＜ log8
a = 7

基本上 log2、log3、log7 這三個要背就是了，高中老師應該都會這樣要求學生吧？

[nicklin9192]

明白了,多謝