Mathematics
Grade9
Easy

Question

I have been given the long leg in this 30-60-90 triangle.  Choose the correct way to  find the short leg.

  1. Multiply 7 by 2
  2. Multiply 7 by square root of 3
  3. Divide 7 by 2
  4. Divide 7 by square root of 3

hintHint:

We are given a right-angled triangle. We are given one of its angle. It is 30°. Then, the other angle will be 60°. We are given the values of its long leg. It is 7. We are asked to find the value of the short leg.

The correct answer is: Divide 7 by square root of 3


    Let the given triangle be ABC.
    ∠ABC = 90°
    ∠BAC = 30°
    AB = y
    BC = 7
    AC = x
    The sum of all angles of a triangle is 180°. Therefore, the remaining angle will be 30°
    So, ∠BCA = 60°
    It is 30°-60°-90° triangle.
    In a 30°-60°-90° triangle, the length of hypotenuse is two times the length of the smallest side. It’s longer side is √3 times the value of the smallest side.
    The side opposite to the 30° angle is the smallest side.
    The side opposite to the 60° angle is the longer side.
    In the given question, the side opposite to 30° is AB.
    Length of smallest side = y
    Hypotenuse = x
    The length of longer side is 7.
    So we can write,
    Length of longer leg = √3 ( length of smaller leg)
    So, to find the smaller leg we have to divide the longer side by √3.

    To solve such questions, we should know the properties of different triangles.

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