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    Hi, I have an equation I need to differentiate, but I'm not sure how;

    x=2dtan(θr)cos(θi)

    d is constant, θi and θr are angles of incidence and refraction, both varying. The question involves finding a maximum x for an angle θi, so I need to differentiate x with respect to θi.
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    If you only vary \theta_i, then \theta_r is constant, so just treat \tan(\theta_r) as a constant.
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    (Original post by around)
    If you only vary \theta_i, then \theta_r is constant, so just treat \tan(\theta_r) as a constant.
    But \theta_r varies as \theta_i varies, so how can you treat is as a constant?
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    (Original post by cameron95)
    But \theta_r varies as \theta_i varies, so how can you treat is as a constant?
    And what rule connects them
 
 
 
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Updated: January 23, 2014
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