Suppose that (๐, ๐) follows a bivariate normal distribution ๐(๐1, ๐2, ๐12, ๐22, ๐) with๐1 = ๐2 = 0 , ๐12 = 1 , ๐22 = 2 , and ๐ = 1/โ2. eet ๐ = ๐๐ + ๐๐ , ๐ = ๐๐ + ๐๐ , findthe four equations that constants ๐, ๐, ๐, ๐ need to satisfy such that ๐ and ๐ areindependent standard normal random variables (no need to solve the equations). (10 points
Question
Suppose that (๐, ๐) follows a bivariate normal distribution ๐(๐1, ๐2, ๐12, ๐22, ๐) with๐1 = ๐2 = 0 , ๐12 = 1 , ๐22 = 2 , and ๐ = 1/โ2. eet ๐ = ๐๐ + ๐๐ , ๐ = ๐๐ + ๐๐ , findthe four equations that constants ๐, ๐, ๐, ๐ need to satisfy such that ๐ and ๐ areindependent standard normal random variables (no need to solve the equations). (10 points
Solution
The conditions for U and V to be independent standard normal random variables are:
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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.
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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/โ2, this simplifies to a^2 + 2b^2 + โ2ab = 1.
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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.
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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/โ2, this simplifies to c^2 + 2d^2 + โ2cd = 1.
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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/โ2, this simplifies to ac + 2bd + โ2(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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