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In the figure above, triangle ABC is inscribed in a circle whose centre O has the x- and y-coordinates as (0,0). If the x- and y- coordinates of point A are (-4,0) and ∠BAC = 30, what is the area, in square units, of triangle AOB?
 
  • a)
    2√3
  • b)
    4√3
  • c)
    8√3
  • d)
    16√3
  • e)
    24√3
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
In the figure above, triangle ABC is inscribed in a circle whose centr...
Given:
O is the center of the circle and A(-4,0) is a point on the circle
  • So, radius of the circle, R = Distance between points O and A = 4 units
  • Also, AC is the diameter of the circle.
S​o, ∠ABC is an angle in the semicircle
  • So, ∠ABC = 90o
  • In right ΔABC,
    • ∠BAC = 30∘
So, by Angle Sum Property, ∠ACB = 60o
To find:
  • Area of (ΔAOB)
Approach:
  • Let’s drop a perpendicular BD from point B on AC.
Area triangle AOB = ½ * AO * BD
  
  • We’ve inferred the length of AO (= radius of the circle) in the Given section above. So, to answer the question, we need to find the length of BD
  • In ΔOBC, sides OB and OC are equal because both are the radii of the circle.
So, this is an isosceles triangle.
  • Since we already know ∠OCB=60, therefore ∠OBC will also be equal to 60.
  • Which finally helps us in inferring that ∠BOC = 60o
  • Hence we can conclude that OBC is an equilateral triangle.
  • The ΔODB, is a 30-60-90 Triangle and we know the measure of radius OB = 4 units. Thus using the side property of 30-60-90 Triangle we can write –
OD: BD: OB = 1: √3: 2
  • BD: OB = √3: 2
  • Thus BD = 2√3
  • Thus area of triangle AOB = ½ * AO * BD = ½ * 4 * 2√3 = 4√3
  • Looking at the answer choices, we see that the correct answer is Option B.
 
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In the figure above, triangle ABC is inscribed in a circle whose centre O has the x- and y-coordinates as (0,0). If the x- and y- coordinates of point A are (-4,0) and ∠BAC = 30∘, what is the area, in square units, of triangle AOB?a)2√3b)4√3c)8√3d)16√3e)24√3Correct answer is option 'B'. Can you explain this answer?
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