JEE MAIN - Mathematics (2020 - 5th September Morning Slot - No. 7)
If the co-ordinates of two points A and B
are $$\left( {\sqrt 7 ,0} \right)$$ and $$\left( { - \sqrt 7 ,0} \right)$$ respectively and
P is any point on the conic, 9x2 + 16y2 = 144, then PA + PB is equal to :
are $$\left( {\sqrt 7 ,0} \right)$$ and $$\left( { - \sqrt 7 ,0} \right)$$ respectively and
P is any point on the conic, 9x2 + 16y2 = 144, then PA + PB is equal to :
8
9
16
6
Explanation
9x2 + 16y2 = 144
$$ \Rightarrow $$ $${{{x^2}} \over {16}} + {{{y^2}} \over 9} = 1$$
$$ \therefore $$ a = 4; b = 3;
Now e = $$\sqrt {1 - {9 \over {16}}} = {{\sqrt 7 } \over 4}$$
A and B are foci
PA + PB = 2a = 2 × 4 = 8
$$ \Rightarrow $$ $${{{x^2}} \over {16}} + {{{y^2}} \over 9} = 1$$
$$ \therefore $$ a = 4; b = 3;
Now e = $$\sqrt {1 - {9 \over {16}}} = {{\sqrt 7 } \over 4}$$
A and B are foci
PA + PB = 2a = 2 × 4 = 8
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