A line passing through the point P(a, 0) makes an acute angle with the positive x-axis. Let this line be rotated about the point P through an angle 2 in the clockwise direction. If in the new position, the slope of the line is 2 - 3 and its distance from the origin is 1 2, then the value of 3a2 2 - 2 3 is :
- 8
- 4
- 5
- 6
Answer
(2) 4
Solution
After a clockwise rotation through 2, the inclination becomes - 2 = 2.
2 = 2 - 3 = 15 = 30 , 2 = 13
New line: y = (2 - 3)(x - a), i.e. (2 - 3)x - y - (2 - 3)a = 0
Distance from O: (2 - 3)|a| 1 + (2 - 3)2 = 1 2
1 + (2 - 3)2 = 8 - 4 3 = 4(2 - 3)
(2 - 3)|a|2 2 - 3 = 1 2 2 - 3 |a| = 2
a2 = 22 - 3 = 2(2 + 3)
3a2 2 - 2 3 = 3 2(2 + 3) 13 - 2 3
= 4 + 2 3 - 2 3 = 4
Answer: (2)