Let the vertex A of a triangle ABC be (1, 2), and the mid-point of the side AB be (5, -1). If the centroid of this triangle is (3, 4) and its circumcenter is ( , ), then 21( + ) is equal to :
- 309
- 403
- 497
- 524
Answer
(3) 497
Solution
Mid-point of AB is (5, -1) B =(2 5-1, 2(-1)-2)=(9, -4)
Centroid (3, 4) C =(3 3-1-9, 3 4-2+4)=(-1, 14)
Circumcentre P( , ): PA2=PB2 and PA2=PC2
PA2=PB2: ( -1)2+( -2)2=( -9)2+( +4)2 4 -3 =23 ...(i)
PA2=PC2: ( -1)2+( -2)2=( +1)2+( -14)2 - +6 =48 ...(ii)
From (ii) =6 -48; in (i): 24 -192-3 =23 = 21521
= 129021- 100821= 28221
21( + )=282+215=497
Answer: (3)