• Given two random variables X and Y, both with nonzero variance, define the function h(t) = E[((X — ux)+t(Y – My))]. (a) Show that h(t) ≥ 0. (b) Show that h(t) = Var(X) + 2 Cov(X, Y)t + Var(Y)t² (c) h is a nonnegative parabola, so it has at most one root. Thus its discriminant is at most 0. Use this to deduce that the correlation coefficient p satisfies -1 ≤p ≤ 1.

Trigonometry (MindTap Course List)
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ISBN:9781337278461
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Chapter6: Topics In Analytic Geometry
Section6.4: Hyperbolas
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Random variables and variance

• Given two random variables X and Y, both with nonzero variance, define the function h(t) = E[((X —
ux)+t(Y – ly))].
(a) Show that h(t) ≥ 0.
(b) Show that h(t) = Var(X) + 2 Cov(X, Y)t + Var(Y)t²
(c) h is a nonnegative parabola, so it has at most one root. Thus its discriminant is at most 0. Use
this to deduce that the correlation coefficient p satisfies −1 ≤ p≤1.
Transcribed Image Text:• Given two random variables X and Y, both with nonzero variance, define the function h(t) = E[((X — ux)+t(Y – ly))]. (a) Show that h(t) ≥ 0. (b) Show that h(t) = Var(X) + 2 Cov(X, Y)t + Var(Y)t² (c) h is a nonnegative parabola, so it has at most one root. Thus its discriminant is at most 0. Use this to deduce that the correlation coefficient p satisfies −1 ≤ p≤1.
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