The problem is to solve the equation $\sin(x - \frac{\pi}{2}) = -\frac{\sqrt{2}}{2}$ for $x$.

AnalysisTrigonometryTrigonometric EquationsSine FunctionPeriodicity
2025/5/29

1. Problem Description

The problem is to solve the equation sin(xπ2)=22\sin(x - \frac{\pi}{2}) = -\frac{\sqrt{2}}{2} for xx.

2. Solution Steps

We are given the equation sin(xπ2)=22\sin(x - \frac{\pi}{2}) = -\frac{\sqrt{2}}{2}.
First, we find the reference angle α\alpha such that sin(α)=22\sin(\alpha) = \frac{\sqrt{2}}{2}.
We know that sin(π4)=22\sin(\frac{\pi}{4}) = \frac{\sqrt{2}}{2}, so α=π4\alpha = \frac{\pi}{4}.
Since sin(xπ2)\sin(x - \frac{\pi}{2}) is negative, xπ2x - \frac{\pi}{2} must be in the third or fourth quadrant. Therefore, we have two cases:
Case 1: xπ2=π+π4+2nπ=5π4+2nπx - \frac{\pi}{2} = \pi + \frac{\pi}{4} + 2n\pi = \frac{5\pi}{4} + 2n\pi, where nn is an integer.
Then, x=5π4+π2+2nπ=5π4+2π4+2nπ=7π4+2nπx = \frac{5\pi}{4} + \frac{\pi}{2} + 2n\pi = \frac{5\pi}{4} + \frac{2\pi}{4} + 2n\pi = \frac{7\pi}{4} + 2n\pi.
Case 2: xπ2=2ππ4+2nπ=7π4+2nπx - \frac{\pi}{2} = 2\pi - \frac{\pi}{4} + 2n\pi = \frac{7\pi}{4} + 2n\pi, where nn is an integer.
Then, x=7π4+π2+2nπ=7π4+2π4+2nπ=9π4+2nπ=π4+2(n+1)π+2π=9π4x = \frac{7\pi}{4} + \frac{\pi}{2} + 2n\pi = \frac{7\pi}{4} + \frac{2\pi}{4} + 2n\pi = \frac{9\pi}{4} + 2n\pi = \frac{\pi}{4} + 2(n+1)\pi + 2\pi = \frac{9\pi}{4}.
Since xπ2x - \frac{\pi}{2} lies in the third or fourth quadrant, we need to consider the angles 5π4\frac{5\pi}{4} and 7π4\frac{7\pi}{4}.
xπ2=5π4+2nπx - \frac{\pi}{2} = \frac{5\pi}{4} + 2n\pi or xπ2=7π4+2nπx - \frac{\pi}{2} = \frac{7\pi}{4} + 2n\pi
x=5π4+π2+2nπ=7π4+2nπx = \frac{5\pi}{4} + \frac{\pi}{2} + 2n\pi = \frac{7\pi}{4} + 2n\pi or x=7π4+π2+2nπ=9π4+2nπ=π4+2(n+1)πx = \frac{7\pi}{4} + \frac{\pi}{2} + 2n\pi = \frac{9\pi}{4} + 2n\pi = \frac{\pi}{4} + 2(n+1)\pi
When n=0n = 0, x=7π4x = \frac{7\pi}{4} or x=9π4x = \frac{9\pi}{4}.
The general solutions are x=7π4+2nπx = \frac{7\pi}{4} + 2n\pi and x=9π4+2nπx = \frac{9\pi}{4} + 2n\pi.
Since sin(xπ/2)=cos(x)\sin(x-\pi/2) = -\cos(x), the equation becomes cos(x)=22-\cos(x) = -\frac{\sqrt{2}}{2} which means cos(x)=22\cos(x) = \frac{\sqrt{2}}{2}. The solutions for this equation are x=π4+2nπx = \frac{\pi}{4} + 2n\pi and x=π4+2nπ=7π4+2(n1)πx = -\frac{\pi}{4} + 2n\pi = \frac{7\pi}{4} + 2(n-1)\pi for integers nn.
Alternatively cos(x)=22\cos(x)=\frac{\sqrt{2}}{2}, thus x=π4+2nπx=\frac{\pi}{4}+2n\pi or x=π4+2nπx=-\frac{\pi}{4}+2n\pi
Then x=π4+2nπx=\frac{\pi}{4}+2n\pi or x=7π4+2nπx=\frac{7\pi}{4}+2n\pi where nn is an integer

3. Final Answer

x=7π4+2nπx = \frac{7\pi}{4} + 2n\pi and x=π4+2nπx = \frac{\pi}{4} + 2n\pi

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