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Please help me on this trigonometry question :(

  • 22-02-2019 9:54am
    #1
    naxmax9
    Registered Users, Registered Users 2 Posts: 134 ✭✭


    The area of the triangle PQR is equal to 48.21cm^2 if |PR| = 15cm and |<PRQ| = 40° find |QR|

    I'm so suck. I know we use the sine rule by how do we use it wit 1 angle and one side?

    What I did is 15sin(40) ÷ 48.21 = 0.1999

    sin inverse 0.1999 = 11.53

    My answer booklet said the answer is 10

    How did they get this answer?


Comments

  • #2
    DavyD_83
    Registered Users, Registered Users 2 Posts: 1,992 ✭✭✭DavyD_83


    Use the area to get perpendicular height
    Then you have a smaller triangle with 2 sides, 15&height;
    1 Angle 40 and a 90 angle.


  • #3
    Framed10
    Registered Users, Registered Users 2 Posts: 240 ✭✭Framed10


    Did you use the area of a triangle formula for trig?
    1/2(a)(b)SinC = 48.21

    1/2 (15)(b) Sin40 =48.21
    (7.5)(b) Sin40 =48.21

    b= 48.21 / 7.5 Sin40


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