A line passes through the point and makes an angle with positive direction of -axis. If it meets the lines represented by at points and , and , then find the number of possible values of .
This is a part of my set Practice for JEE 2017.
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Any point on the line making an angle θ with the x-axis and passing through the point ( 2 , 3 ) can be represented by ( 2 + r cos ( θ ) , 3 + r sin ( θ ) ) where ∣ r ∣ is the distance of the point from ( 2 , 3 ) .
Since we are interested in the intersection of this line with the given pair of straight lines, the above point satsfies the equation of the pair of straight lines:
( 2 + r cos ( θ ) ) 2 − 2 ( 2 + r cos ( θ ) ) ( 3 + r sin ( θ ) ) − ( 3 + r sin ( θ ) ) 2 = 0
r 2 ( sin θ − cos θ ) 2 + 2 r ( sin θ − cos θ ) − 1 7 = 0
Since the moduli of the roots of the above equation are the distances of the intersection points from ( 2 , 3 ) :
∣ ∣ ∣ ∣ ∣ ( sin θ − cos θ ) 2 − 1 7 ∣ ∣ ∣ ∣ ∣ = 1 7
⟹ ( sin θ − cos θ ) 2 = 1
⟹ 1 − 2 sin θ cos θ = 1
⟹ s i n θ cos θ = 0
θ = 0 , 2 π