Solving problems using Half Angle identities

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SUMMARY

The discussion focuses on solving the equation cos(x/2) = -√2 / 2 using half-angle identities. The relevant identity used is cos(x/2) = ± √(1 + cos x) / 2. By substituting u = x/2, the equation simplifies to 1 + cos(x) = 0, leading to the conclusion that cos(x) = -1. This results in the solutions x = 270 degrees or 3π/2.

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  • Understanding of trigonometric identities, specifically half-angle identities.
  • Familiarity with solving trigonometric equations.
  • Knowledge of the unit circle and angle measures in degrees and radians.
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  • Study the derivation and applications of half-angle identities in trigonometry.
  • Practice solving various trigonometric equations using different identities.
  • Explore the unit circle to better understand angle measures and their corresponding trigonometric values.
  • Learn about the graphical representation of trigonometric functions to visualize solutions.
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Homework Statement



Solve for x using half-angle identities

cos (x/2) = -√2 / 2

Homework Equations



cos(x/2) = ± √(1+cosx)/2

The Attempt at a Solution



I am trying to figure out what to do with the identity, but I have no idea how to start. I know that x = 270 degrees or 3pi/2, but I do not know how to get there. Can someone head me in the right direction?
 
Last edited:
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cos2u= (1+ cos 2u)/2

Let u= x/2. Then [itex](1+ cos x)/2= (-\sqrt{2}/2)^2= 1/2[/itex] so 1+ cos(x)= 0, cos(x)= -1.
 
Thank you so much
 

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