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Math Help - triangle trigonometry

  1. #1
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    triangle trigonometry




    Figure 1 shows the triangle ABC, with AB=6cm, BC=4cm and CA=5cm

    a) show that cosA=3/4

    b) hence, or otherwise, find the exact value of sinA


    thx!
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  2. #2
    MHF Contributor Mathstud28's Avatar
    Joined
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    here is how I would do this

    c^2=a^2+b^2-2abcos(\theta) imput correct values and solve for \theta...and for the second one use the law of sines which says that \frac{a}{sin(A)}=\frac{b}{sin(B)}=\frac{c}{sin(C)} where caps are angles and lower case are sides
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