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Question -

Find the equation of the circle passing through (0, 0) and making intercepts a and b on the coordinate axes.



Answer -

Let the equation of the requiredcircle be (x┬атАУ┬аh)2┬а+ (y┬атАУ┬аk)2┬а=┬аr2.

Sincethe circle passes through (0, 0),

(0тАУ┬аh)2┬а+ (0 тАУ┬аk)2┬а=┬аr2

тЗТ┬аh2┬а+┬аk2┬а=┬аr2

Theequation of the circle now becomes (x┬атАУ┬аh)2┬а+ (y┬атАУ┬аk)2┬а=┬аh2┬а+┬аk2.

Itis given that the circle makes intercepts┬аa┬аand┬аb┬аonthe coordinate axes. This means that the circle passes through points (a,0) and (0,┬аb). Therefore,

(a┬атАУ┬аh)2┬а+ (0 тАУ┬аk)2┬а=┬аh2┬а+┬аk2┬атАж(1)

(0тАУ┬аh)2┬а+ (b┬атАУ┬аk)2┬а=┬аh2┬а+┬аk2┬атАж (2)

Fromequation (1), we obtain

a2┬атАУ 2ah┬а+┬аh2┬а+┬аk2┬а=┬аh2┬а+┬аk2

тЗТ┬аa2┬атАУ 2ah┬а= 0

тЗТ┬аa(a┬атАУ2h)= 0

тЗТ┬аa┬а=0 or (a┬атАУ2h)= 0

However,┬аa┬атЙа0; hence, (a┬атАУ2h)= 0 тЗТ┬аh┬а=.

Fromequation (2), we obtain

h2┬а+┬аb2┬атАУ2bk┬а+┬аk2┬а=┬аh2┬а+┬аk2

тЗТ┬аb2┬атАУ 2bk┬а= 0

тЗТ┬аb(b┬атАУ2k)= 0

тЗТ┬аb┬а=0 or(b┬атАУ2k)= 0

However,┬аb┬атЙа0; hence, (b┬атАУ2k)= 0 тЗТ┬аk┬а=┬а.

Thus,the equation of the required circle is

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