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Maths Problem

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  • 04-11-2009 12:32am
    #1
    jumpguy
    Registered Users Posts: 7,962 ✭✭✭


    Was revising maths tonight and I came across a problem. I couldn't for the life of me remember what to do. So I turn to you all-knowing boardsies for help!

    For those of you with Text and Tests 4, it's Exercise 2C Question 11 and 12

    Q11. If Cos A = -11/13 and sin A is positive, express Tan A as a fraction.

    I know it's related to the unit circle, but I can't covert the Cos into degrees :confused:

    Q12. If Cos A = 0.7986 and Tan A is negative, find the value of sin A. (0 Degrees is Less Than A which is Less Than 360 Degrees).



    Please explain how to do 'em, the answer is of no help (just revising, not h/w). Thanks in advance! :)


Comments

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    #2
    Johnny Giles
    Closed Accounts Posts: 771 ✭✭✭Johnny Giles


    H/L Maths.

    God No.


  • Options
    #3
    clartharlear
    Registered Users Posts: 489 ✭✭clartharlear


    Because cos is negative and sin is positive, from the unit circle, you know that tan is negative.

    Draw a right-angled triangle for which Cos A = 11/13 [C = A/H] and use Pythagoras to find the third side (opposite).

    Tan A = O/A.

    Leave the answer in surd form since they ask you for a fraction.

    Tan A = -(sqrt48)/11


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    #4
    blubloblu
    Registered Users Posts: 1,226 ✭✭✭blubloblu


    Tan = sin/cos
    how could it possibly be positive?
    And cos is A/H. Which makes that a 11,12,13 triangle, much easier.


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