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Question -

Find the equation of the set of points P, the sum of whose distances from A (4, 0, 0) and B (тАУ4, 0, 0) is equal to 10.



Answer -

Let the coordinates of P be (x,┬аy,┬аz).

The coordinates of points A and B are (4, 0, 0) and (тАУ4, 0, 0) respectively.

It is given that PA + PB = 10.

Onsquaring both sides, we obtain

Onsquaring both sides again, we obtain

25 (x2┬а+8x┬а+ 16 +┬аy2┬а+┬аz2) = 625 + 16x2┬а+ 200x

тЗТ 25x2┬а+ 200x┬а+400 + 25y2┬а+25z2┬а=625 + 16x2┬а+200x

тЗТ 9x2┬а+ 25y2┬а+ 25z2┬атАУ 225 = 0

Thus, therequired equation is 9x2┬а+ 25y2┬а+ 25z2┬атАУ 225 = 0.

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