
Concept explainers
To find the third vertices of equilateral

Answer to Problem 13.12EX
Option (b)
Explanation of Solution
Given information: Vertices of the triangle are: (r, 0) and (−r, 0) .
Concept used:
The distance between the points (x1,y1) and (x2,y2) is
√(x2−x1)2+(y2−y1)2
Let ABC be the triangle with vertices as A(r, 0), B(−r, 0) and C(a, b) .
Using distance formula,
AB=√4r2=2r; BC=√(a+r)2+b2; AC=√(a−r)2+b2
For an equilateral triangle, AB = BC = AC
(a+r2)+b2=(a−r2)+b2a2+r2+2ar+b2=a2+r2−2ar+b24ar=0⇒ a=0
Also,
√r2+b2=√4r2r2+b2=4r23r2=b2b=r√3
Hence, the third coordinate of the equilateral triangle is (0, r√3) .
Chapter E Solutions
McDougal Littell Jurgensen Geometry: Student Edition Geometry
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