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Find the value of theta in (pi/2,pi) if cos theta = -12/5

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potziunea | Student, Grade 10 | (Level 2) Honors

Posted July 22, 2011 at 10:43 PM via web

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Find the value of theta in (pi/2,pi) if cos theta = -12/5

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giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted July 22, 2011 at 10:46 PM (Answer #1)

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It is impossible for a cosine of an angle to be smaller than -1.

We notice that cos `theta` =-12/5 = -2.4 < -1

Therefore, there is no value for `theta` in the given interval (`pi` /2 ; `pi` ), for cos `theta` = -12/5.

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted July 22, 2011 at 11:07 PM (Answer #2)

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You have given that cos theta = -12/5 and we have to determine the values of theta that satisfy the relation.

-12/5 = -2.4

But the cosine of any number lies in the interval [-1, 1]

Therefore there can be no theta such that cos theta = -12/5

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