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Math Help - triangle proof

  1. #1
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    triangle proof

    you have an isosceles triangle whose angle is x and the two equal sides are s. show that the area of the triangle is given by A=1/2 s^2 sinx.

    I got 1/2 s sinx but i cant get s^2 can someone help? i greatly appreciate it.
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  2. #2
    Member u2_wa's Avatar
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    Quote Originally Posted by soldatik21 View Post
    you have an isosceles triangle whose angle is x and the two equal sides are s. show that the area of the triangle is given by A=1/2 s^2 sinx.

    I got 1/2 s sinx but i cant get s^2 can someone help? i greatly appreciate it.
    Suppose sides of triangle as A,B&C
    Side AB=AC
    \angle{BAC}=x
    \angle{ABC}=90-\frac{x}{2}
    Area = \frac{1}{2}(s.sin(90-\frac{x}{2}))(2s.cos(90-\frac{x}{2}))
    sin2x=2sinx.cosx
    \frac{1}{2}sin(180-x)=sin(90-\frac{x}{2}).cos(90-\frac{x}{2})
    As sin(180-x)=sinx<br />
    Hence, Area = \frac{1}{2}.s^2.sinx
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