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Algebra Difficulty 3.3 AMC 10/12 Find the answer

How many ordered pairs (a,b)(a,b) such that aa is a positive real number and bb is an integer between 22 and 200200, inclusive, satisfy the equation (logba)2017=logb(a2017)?(\log_b a)^{2017}=\log_b(a^{2017})?

Pick one

Solution

By the properties of logarithms, we can rearrange the equation to read x2017=2017xx^{2017}=2017x with x=logbax=\log_b a. If x0x\neq 0, we may divide by it and get x2016=2017x^{2016}=2017, which implies x=±\root2016\of2017x=\pm \root{2016}\of{2017}. Hence, we have 33 possible values xx, namely
x=0,x=201712016,andx=201712016.x=0,\qquad x=2017^{\frac1{2016}},\, \text{and}\quad x=-2017^{\frac1{2016}}.
Since logba=x\log_b a=x is equivalent to a=bxa=b^x, each possible value xx yields exactly 199199 solutions (b,a)(b,a), as we can assign a=bxa=b^x to each b=2,3,,200b=2,3,\dots,200. In total, we have 3199=(E) 5973\cdot 199=\boxed{\textbf{(E) } 597} solutions.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.