Let (5, a4 ) be the circumcenter of a triangle with vertices A(a,-2), B(a, 6) and C ( a4,-2 ). Let denote the circumradius, denote the area and denote the perimeter of the triangle. Then + + is
- 60
- 62
- 53
- 30
Answer
(3) 53
Solution
Circumcentre O: OA=OB
(a-5)2+ ( a4+2 )2=(a-5)2+ ( a4-6 )2
a4+2=6- a4 a=8
∴ A(8,-2), B(8,6), C(2,-2), O(5,2)
[figure]
AB=8 (vertical), AC=6 (horizontal) A=90 , BC=10
∵ O is the mid-point of hypotenuse BC: = BC2=5
= 12 8 6=24, =8+6+10=24
+ + =5+24+24=53
Answer: (3)