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Find the following trigonometric values.
Express your answers exactly.

{:[cos((7pi)/(4))=],[sin((7pi)/(4))=]:}

Find the following trigonometric values.\newlineExpress your answers exactly.\newlinecos(7π4)=sin(7π4)= \begin{array}{l} \cos \left(\frac{7 \pi}{4}\right)= \\ \sin \left(\frac{7 \pi}{4}\right)= \end{array}

Full solution

Q. Find the following trigonometric values.\newlineExpress your answers exactly.\newlinecos(7π4)=sin(7π4)= \begin{array}{l} \cos \left(\frac{7 \pi}{4}\right)= \\ \sin \left(\frac{7 \pi}{4}\right)= \end{array}
  1. Understand the unit circle: Understand the unit circle and the values of cosine and sine for special angles.\newlineThe unit circle allows us to find the values of sine and cosine for multiples of π/4\pi/4, π/2\pi/2, π\pi, and so on. The angles (7π/4)(7\pi/4) and (π/4)(\pi/4) are coterminal, meaning they share the same terminal side on the unit circle. Therefore, cos((7π/4))\cos((7\pi/4)) and sin((7π/4))\sin((7\pi/4)) will have the same absolute values as cos((π/4))\cos((\pi/4)) and sin((π/4))\sin((\pi/4)), but possibly different signs depending on the quadrant in which the angle (7π/4)(7\pi/4) lies.
  2. Determine the quadrant: Determine the quadrant in which the angle (7π/4)(7\pi/4) lies.\newlineThe angle (7π/4)(7\pi/4) is more than 2π2\pi but less than 2π+π/42\pi + \pi/4, which means it is in the fourth quadrant of the unit circle. In the fourth quadrant, cosine is positive and sine is negative.
  3. Calculate cos(7π4)\cos\left(\frac{7\pi}{4}\right): Calculate the value of cos(7π4)\cos\left(\frac{7\pi}{4}\right).\newlineSince 7π4\frac{7\pi}{4} is coterminal with π4\frac{\pi}{4}, and we know that cos(π4)=22\cos\left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}, we can say that cos(7π4)=22\cos\left(\frac{7\pi}{4}\right) = \frac{\sqrt{2}}{2} because cosine is positive in the fourth quadrant.
  4. Calculate sin(7π4)\sin\left(\frac{7\pi}{4}\right): Calculate the value of sin(7π4)\sin\left(\frac{7\pi}{4}\right). Similarly, since 7π4\frac{7\pi}{4} is coterminal with π4\frac{\pi}{4}, and we know that sin(π4)=22\sin\left(\frac{\pi}{4}\right) = \frac{\sqrt{2}}{2}, we can say that sin(7π4)=22\sin\left(\frac{7\pi}{4}\right) = -\frac{\sqrt{2}}{2} because sine is negative in the fourth quadrant.

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