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Anti-trigonometric Function Problem

Source: 1986 National High School Mathematics League, Exam One, Problem 1

February 24, 2020
functioninequalities

Problem Statement

Let 1<a<0-1<a<0, θ=arcsina\theta=\arcsin a. Then the solution set to the inequality sinx<a\sin x<a is (A){x2nπ+θ<x<(2n+1)πθ,nZ}\text{(A)}\{x|2n\pi+\theta<x<(2n+1)\pi-\theta,n\in\mathbb{Z}\} (B){x2nπθ<x<(2n+1)π+θ,nZ}\text{(B)}\{x|2n\pi-\theta<x<(2n+1)\pi+\theta,n\in\mathbb{Z}\} (C){x(2n1)π+θ<x<2nπθ,nZ}\text{(C)}\{x|(2n-1)\pi+\theta<x<2n\pi-\theta,n\in\mathbb{Z}\} (D){x(2n1)πθ<x<2nπ+θ,nZ}\text{(D)}\{x|(2n-1)\pi-\theta<x<2n\pi+\theta,n\in\mathbb{Z}\}