AP EAMCET202120 Aug 2021Morning ShiftMathematicsStraight LinesActual
The equation of a straight line which passes through the point a cos 3 θ , a sin 3 θ and perpendicular to x secθ + y c o s e c θ = a is
Options
- Ax a + y a = a cosθ
- Bx cosθ - y sinθ = a cos 2 θ
- Cx cosθ + y sinθ = a cos 2 θ
- Dx cosθ + y sinθ - a cos 2 θ = 1
Correct answer
B. x cosθ - y sinθ = a cos 2 θ
Step-by-step solution
We know that a line perpendicular to the line a x + b y + c = 0 is given by b x - a y + k = 0 . Here, given line x sec θ + y cosec θ = a . So, the perpendicular line is x cosec θ - y sec θ + k = 0 . The point a cos 3 θ , a sin 3 θ lies on the line ⇒ a cos 3 θ sin θ - a sin 3 θ cos θ = - k ⇒ a cos 4 θ - sin 4 θ sin θ cos θ = - k ⇒ a cos 2 θ - sin 2 θ cos 2 θ + sin 2 θ sin θ cos θ = - k Using cos 2 &#