Let a be the length of a side of a square OABC with O being the origin. Its side OA makes an acute angle with the positive x-axis and the equations of its diagonals are ( 3+1)x + ( 3-1)y = 0 and ( 3-1)x - ( 3+1)y + 8 3 = 0. Then a2 is equal to :
- 48
- 16
- 24
- 32
Answer
(1) 48
Solution
The diagonal through O is OB: ( 3+1)x + ( 3-1)y = 0.
The other diagonal AC: ( 3-1)x - ( 3+1)y + 8 3 = 0 (it does not pass through O).
The diagonals of a square bisect each other at right angles, the distance of O from AC is half of the diagonal OB = a 22 = a 2.
Distance of O from AC = 8 3 ( 3-1)2 + ( 3+1)2 = 8 3 8 = 2 6
a 2 = 2 6 a = 4 3
a2 = 48
Answer: (1)