AlgebraDifficulty 4.2AIMEFind the answerUnited States
Let x be the least real number greater than 1 such that sinx=sin(x2), where the arguments are in degrees. What is x rounded up to the closest integer?
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Solution
Answer (B): The given condition means that either x and x2 represent the same angle or they represent supplementary angles. In the first case x2=x+360k for some integer k. By the quadratic formula, x=21±1+1440k. The least value of x>1 occurs when k=1 and the plus sign is used, in which case x=21+1441. In the second case x2+x=180(2k+1) for some integer k. By the quadratic formula, x=2−1±1−720(2k+1). The least value of x>1 occurs when k=−1 and the plus sign is used, in which case x=2−1+721. Because 272=729>721 and 252=625<721, the value of x rounds up to 2−1+27=13, which is smaller than the value of x obtained from the first case.
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