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3 years ago

8x^4+24x^3-27x-81 what is the polynomial factor?

1 answer:

3 0

$8x^4+24x^3-27x-81=8x^3(x+3)-27(x+3)\\\\=(x+3)(8x^3-27)=(x+3)(2^3x^3-3^3)=(x+3)[(2x)^3-3^3]\\\\\text{use}\ a^3-b^3=(a-b)(a^2+ab+b^2)\\\\=(x+3)(2x-3)[(2x)^2+(2x)(3)+3^2]\\\\=\boxed{(x+3)(2x-3)(4x^2+6x+9)}$

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If X is a r.v. such that E(X^n)=n! Find the m.g.f. of X,Mx(t). Also find the ch.f. of X,and from this deduce the distribution of

astraxan [27]

$M_X(t)=\mathbb E(e^{Xt})$
$M_X(t)=\mathbb E\left(1+Xt+\dfrac{t^2}{2!}X^2+\dfrac{t^3}{3!}X^3+\cdots\right)$
$M_X(t)=\mathbb E(1)+t\mathbb E(X)+\dfrac{t^2}{2!}\mathbb E(X^2)+\dfrac{t^3}{3!}\mathbb E(X^3)+\cdots$
$M_X(t)=1+t+t^2+t^3+\cdots$
$M_X(t)=\displaystyle\sum_{k\ge0}t^k=\frac1{1-t}$

provided that $|t|$ .

Similarly,

$\varphi_X(t)=\mathbb E(e^{iXt})$
$\varphi_X(t)=1+it+(it)^2+(it)^3+\cdots$
$\varphi_X(t)=(1-t^2+t^4-t^6+\cdots)+it(1-t^2+t^4-t^6+\cdots)$
$\varphi_X(t)=(1+it)(1-t^2+t^4-t^6+\cdots)$
$\varphi_X(t)=\dfrac{1+it}{1+t^2}=\dfrac1{1-it}$

You can find the CDF/PDF using any of the various inversion formulas. One way would be to compute

$F_X(x)=\displaystyle\frac12+\frac1{2\pi}\int_0^\infty\frac{e^{itx}\varphi_X(-t)-e^{-itx}\varphi_X(t)}{it}\,\mathrm dt$

The integral can be rewritten as

$\displaystyle\int_0^\infty\frac{2i\sin(tx)-2it\cos(tx)}{it(1+t^2)}\,\mathrm dt$

so that

$F_X(x)=\displaystyle\frac12+\frac1{2\pi}\int_0^\infty\frac{\sin(tx)-t\cos(tx)}{t(1+t^2)}\,\mathrm dt$

There are lots of ways to compute this integral. For instance, you can take the Laplace transform with respect to $x$ , which gives

$\displaystyle\mathcal L_s\left\{\int_0^\infty\frac{\sin(tx)-t\cos(tx)}{t(1+t^2)}\,\mathrm dt\right\}=\int_0^\infty\frac{1-s}{(1+t^2)(s^2+t^2)}\,\mathrm dt$
$=\displaystyle\frac{\pi(1-s)}{2s(1+s)}$

and taking the inverse transform returns

$F_X(x)=\dfrac12+\dfrac1\pi\left(\dfrac\pi2-\pi e^{-x}\right)=1-e^{-x}$

which describes an exponential distribution with parameter $\lambda=1$ .

6 0

3 years ago

PLEASE HELP WILL MARK BRANLIEST. There are twelve shirts in your closet, four blue and eight green. You randomly select one to w

lbvjy [14]

Answer:

$\frac{4}{8} = \frac{2}{4}$

7 0

3 years ago

#if a sum become rs 6480 in 3 years and rs 7776 in 4 years interest being compounded annually, find the sum and rate of interest

Andrei [34K]

Answer:

The rate of interest is 20% and the sum is $3,750

Step-by-step explanation:

In order to calculate the sum and rate of interest we would have to make the following calculation:

rate of interest= (sum in 4 years-sum in 3 years)*100/sum in 3 years*1

According to the given data we have the following:

sum in 4 years=$7,776

sum in 3 years=$6,480

Therefore, sum in 4 years-sum in 3 years=$7,776-$6,480=$1,296

Therefore, rate of interest=$1,296*100/$6,480*1

rate of interest=20%

To calculate the sum we would have to make the following calculation:

FV=PV(1+20%)∧3

$6,480=PV(1,20)∧3

PV=$3,750

Sum is $3,750

8 0

3 years ago

8× what =2

sergejj [24]

Answer:

8*1/4= 2

A) 0.071

B) 0.48

5 0

3 years ago

What is the coefficient in the expression 10x + 8 I need help

koban [17]

Answer:

Step-by-step explanation:

A coefficient is a multiplicative factor. Whatever is in front of the variable is a coefficient

5 0

3 years ago