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Question
Suppose error involved in making a certain measurement is a continuous r. v. X with p.d.f.
f(x) = `{("k"(4 - x^2), "for" -2 ≤ x ≤ 2),(0, "otherwise".):}`
compute P(–1 < X < 1)
Solution
Given that f(x) represents a p.d.f. of r.v. X.
∴ `int_-2^2 f(x)*dx` = 1
∴ `int_-2^2 "k"(4 - x^2)*dx` = 1
∴ `"k"[4x - x^3/3]_-2^2` = 1
∴ `"k"[(8 - 8/3) - (-8 + 8/3)]` = 1
∴ `"k"(16/3 + 16/3)` = 1
∴ `"k"(32/3)` = 1
∴ k = `(3)/(32)`
F(x) = `int_-2^2 f(x)*dx`
= `int_-2^2"k"(4 - x^2)*dx`
= `(3)/(32)[4x - x^3/3]_-2^2`
= `(3)/(32)[4x - x^3/3 + 8 - 8/3]`
∴ F(x) = `(3)/(32)[4x - x^3/3 + 16/3]`
P(–1 < X < 1) = F(1) – F(–1)
= `(3)/(32)(4 - 1/3 + 16/3) - (3)/(32)(-4 + 1/3 + 16/3)`
= `(3)/(32)(9 - 5/3)`
= `(3)/(32)(22/3)`
= `(11)/(16)`.
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