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Two regression lines are perpendicular when
Ar = 0
Bbyx = bxy
Cr = 1
Dbyx = 1
Answer & Solution
Correct answer: A. r = 0
1. The angle between regression lines depends on r.
2. They coincide when r = 1 (or -1) and are perpendicular when r = 0.
3. At r = 0, byx = 0 and bxy = 0; lines become y = ybar and x = xbar.
4. These are perpendicular axes; hence r = 0 gives perpendicular regression lines.
_Source: ICAI BoS Foundation Paper 3, Ch 17 'Regression', p.13_
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