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Transcript

Example 3 Find the centre and the radius of the circle x2 + y2 + 8x + 10y – 8 = 0 Given x2 + y2 + 8x + 10y − 8 = 0 We need to make this in form (x – h)2 + (y – k)2 = r2 From (1) x2 + y2 + 8x + 10y − 8 = 0 (x2 + 8x) + (y2 + 10y) = 8 (x)2 + 2(4)(x) + y2 + 2(5)(y) = 8 [x2 + 2(4)(x) + (4)2 − (4)2] + [y2 + 2(5)(y) + (5)2 − (5)2] = 8 [x2 + 2(4)(x) + (4)2] + [y2 + 2(5)(y) + (5)2] − (4)2 − (5)2 = 8 (x + 4)2 + (y + 5)2 = 8 + 16 + 25 (x + 4)2 + (y + 5)2 = 49 (x – (– 4))2 + (y – (–5))2 = 72 Comparing (2) with (x – h)2 + (y – k)2 = r2 h = −4 , k = − 5 & r = 7 Thus, centre of circle = (h, k) = (−4, −5) & Radius = r = 7

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.