Re: [微積] 微積分基本定理的題目
※ 引述《EvilKnight (邪黯)》之銘言:
: x
: Let f:(0,∞)→R and f(x)=∫(1/t)dt
: 1
: Use the Fundamental Theorem of Calculus to show that,
: for all a,b屬於(0,∞),
: f(ab) = f(a) + f(b)
(sol) x
f(x)=∫(1/t)dt
1
From the Fundamental Theorem of Calculus, we have
f'(x) = 1/x => f(x) = ln(x) + c , x > 0
=> f(ab) = ln(ab) + c = ln(a) + ln(b) + c_
= f(a) + f(b)
請教一下這題該怎麼解?
: 有想過透過定理讓式子變成 f'(x)=1/x
: 可是這樣f'(ab)不等於f'(a)+f'(b)耶 @@
: Hint說:
: give a>0
: Let g(x)=f(ax)-f(a)-f(x),x>0 ...
: 可是我看不懂為什麼會這樣列式,也不知道應該怎麼做下去...
: 感謝幫忙~
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