Engineering
Mathematics
Tangent to Ellipse

Question

Tangents are drawn from the point P(3, 4) to the ellipse  touching the ellipse at points A and B.

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Linked Question 1

The equation of the locus of the point whose distances from the point P and the line AB are equal, is

9x2 + 9y2 – 6xy – 54x – 62y – 241 = 0

x2 + y2 – 2xy + 27x + 31y – 120 = 0

x2 + 9y2 + 6xy – 54x + 62y – 241 = 0

9x2 + y2 – 6xy – 54x – 62y + 241 = 0

Solution

Straight line AB :

 y0=13(x3)

Applying x + 3y = 3

Applying PS = SM

 (h3)2+(k4)2=|h+3k310|2

       Locus of S(h, k) is

10(x2 + y2 – 6x – 5y + 25) = x2 + 9y2 + 6xy + 9 – 6(x + 3y)

9x2 + y2 – 6xy – 54x – 62y + 241 = 0

 

Linked Question 2

The coordinates of A and B are

 (85,  216115)  and  (95,  85)

(3. 0) and (0. 2)

 (85,  216115)  and  (0,  2)

 (3,  0)  and  (95,  85)

Solution

Clearly A is (3, 0)

 y=mx±9m2+4

 43m=±9m2+4

16 + 9m2 – 24m = 9m2 + 4

 12=24mm=12

 y=12x+94+4

2y = x + 5

Let Be be (x1, y1)

equation of tangent at B

 xx19+yy14=1x2y=5}      x19·1=y14(2)=15

 x1=95,y1=85

 

Linked Question 3

The orthocenter of the triangle PAB is

 (825,  725)

 (5,  87)

 (115,  85)

 (75,  258)

Solution

 mAB=850953=824=13

          Altitude P2 :  y – 4 = 3(x – 3)

     3x – y = 5          ....(1)

Altitude BM : y = 85                   ....(2)

Solving (1) and (2):  (115,  85)