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3 years ago

X +4= 2x I need help

2 answers:

8 0

Combine like terms by subtracting x from both sides.
x + 4 = 2x
4 = 2x - x
4 = x

(On one side, x-x cancelled out, and on the other side, the 2x-x works like normal subtraction so you are left with x. Therefore x is 4)

Naddika [18.5K]3 years ago

7 0

Step-by-step explanation:

To solve this problem

collect like terms

x-2x = -4

-x =-4

divide both sides of the equation by -

-x /- =-4

x=4

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$\mathrm{Var}[X]=E[(X-E[X])^2]=E[X^2-2XE[X]+E[X]^2]=E[X^2]-E[X]^2$

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$E[X^2]=\displaystyle\int_{-\infty}^\infty x^2f_X(x)\,\mathrm dx=\frac29\int_0^\infty x^3e^{-x^2/9}\,\mathrm dx$

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$u=x^2\implies\mathrm du=2x\,\mathrm dx$

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$E[X^2]=\displaystyle-x^2e^{-x^2/9}\bigg|_0^\infty+2\int_0^\infty xe^{-x^2/9}\,\mathrm dx$

$E[X^2]=\displaystyle2\int_0^\infty xe^{-x^2/9}\,\mathrm dx$

Substitute $x=3y^{1/2}$ again to get

$E[X^2]=\displaystyle9\int_0^\infty e^{-y}\,\mathrm dy=9$

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