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Suppose that (๐‘‹, ๐‘Œ) follows a bivariate normal distribution ๐‘(๐œ‡1, ๐œ‡2, ๐œŽ12, ๐œŽ22, ๐œŒ) with๐œ‡1 = ๐œ‡2 = 0 , ๐œŽ12 = 1 , ๐œŽ22 = 2 , and ๐œŒ = 1/โˆš2. eet ๐‘ˆ = ๐‘Ž๐‘‹ + ๐‘๐‘Œ , ๐‘‰ = ๐‘๐‘‹ + ๐‘‘๐‘Œ , findthe four equations that constants ๐‘Ž, ๐‘, ๐‘, ๐‘‘ need to satisfy such that ๐‘ˆ and ๐‘‰ areindependent standard normal random variables (no need to solve the equations). (10 points

Question

Suppose that (๐‘‹, ๐‘Œ) follows a bivariate normal distribution ๐‘(๐œ‡1, ๐œ‡2, ๐œŽ12, ๐œŽ22, ๐œŒ) with๐œ‡1 = ๐œ‡2 = 0 , ๐œŽ12 = 1 , ๐œŽ22 = 2 , and ๐œŒ = 1/โˆš2. eet ๐‘ˆ = ๐‘Ž๐‘‹ + ๐‘๐‘Œ , ๐‘‰ = ๐‘๐‘‹ + ๐‘‘๐‘Œ , findthe four equations that constants ๐‘Ž, ๐‘, ๐‘, ๐‘‘ need to satisfy such that ๐‘ˆ and ๐‘‰ areindependent standard normal random variables (no need to solve the equations). (10 points

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Solution

The conditions for U and V to be independent standard normal random variables are:

  1. E[U] = E[aX + bY] = 0 This implies that aE[X] + bE[Y] = 0. Given that E[X] = E[Y] = 0, this equation is always satisfied for any a and b.

  2. Var[U] = Var[aX + bY] = 1 This implies that a^2Var[X] + b^2Var[Y] + 2ab*Cov[X,Y] = 1. Given that Var[X] = 1, Var[Y] = 2, and Cov[X,Y] = ฯ = 1/โˆš2, this simplifies to a^2 + 2b^2 + โˆš2ab = 1.

  3. E[V] = E[cX + dY] = 0 This implies that cE[X] + dE[Y] = 0. Given that E[X] = E[Y] = 0, this equation is always satisfied for any c and d.

  4. Var[V] = Var[cX + dY] = 1 This implies that c^2Var[X] + d^2Var[Y] + 2cd*Cov[X,Y] = 1. Given that Var[X] = 1, Var[Y] = 2, and Cov[X,Y] = ฯ = 1/โˆš2, this simplifies to c^2 + 2d^2 + โˆš2cd = 1.

  5. Cov[U,V] = Cov[aX + bY, cX + dY] = 0 This implies that acVar[X] + bdVar[Y] + (ad+bc)*Cov[X,Y] = 0. Given that Var[X] = 1, Var[Y] = 2, and Cov[X,Y] = ฯ = 1/โˆš2, this simplifies to ac + 2bd + โˆš2(ad+bc) = 0.

These are the four equations that the constants a, b, c, and d need to satisfy for U and V to be independent standard normal random variables.

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