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March 30, 2017

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Find secx if sinx = -4/5 and 270 < x < 360.

tan^2x+1=sec^2x
(-4/5)^2+1=sec^2x
16/25+1=sec^2x
17/25=sec^2x
sqrt 17/5

I don't know if it should be positive or negative.

  • Trig - ,

    You are in the fourth quadrant
    the secant has the same sign as the cosine, and in the fourth quadrant the cosine is positive,

    Your answer is not correct

    Here is an easier way than trying to use the formula you tried.
    sinß = y/r = -4/5
    so x^2 + (-4)^2 = 5^2
    x = ±3 but you are in the fourth quadr, so x=+3
    sec x = 1/cosx = 1/(3/5) = 5/3

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