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2 years ago

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Consider the expressions below. for each expression below, select the letter that corresponds to the equivalent expression given

above. is equivalent to expression . is equivalent to expression . is equivalent to expression . is equivalent to expression .

1 answer:

Karo-lina-s [1.5K]2 years ago

5 0

The considerations of expressions for each expressions are shown below.

<h3>What is an expression?</h3>

An expression in mathematics is a combination of numbers, variables, and functions (such as addition, subtraction, multiplication or division, etc.)
Expressions and phrases are similar in structure.
In English, a phrase may involve action on its own, but it does not constitute a whole sentence.

To consider the expressions:

Part 1:

(x²+15x+65)+(2x-5)*(3x+8)
(x²+15x+65)+(6x²+16x-15x-40)
(7x²+16x+25)

The answer to Part 1 is the letter B,

(7x²+16x+25)

Part 2:

(4x+1)*(3x-4)-(5x²-10x-12)
(4x+1)*(3x-4)-(5x²-10x-12)
(12x²-16x+3x-4)-(5x²-10x-12)
(7x²-3x+8)

The answer to Part 2 is the letter D,

(7x²-3x+8)

Part 3:

(8x²+19x+4)+(3x+2)*(x-5)
(8x²+19x+4)+(3x²-15x+2x-10)
(11x²+6x-6)

The answer to part 3 is the letter A,

(11x²+6x-6)

Part 4:

(6x+1)*(3x-7)-(7x²-34x-20)
(18x²-42x+3x-7)-(7x²-34x-20)
(11x²-5x+13)

The answer to part 4 is the letter C,

(11x²-5x+13)

Therefore, the considerations of expressions for each expression are shown.

Know more about expressions here:

brainly.com/question/24734894

#SPJ4

The complete question is given below:
For each expression below, select the letter that corresponds to the equivalent expression given above.

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2 years ago

A building has n floors numbered 1,2,...,n, plus a ground floor g. at the ground floor, m people get on the elevator together, a

fomenos

Let $X_i$ be the random variable indicating whether the elevator does not stop at floor $i$ , with

$X_i=\begin{cases}1&\text{if the elevator does not stop at floor }i\\0&\text{otherwise}\end{cases}$

Let $Y$ be the random variable representing the number of floors at which the elevator does not stop. Then

$Y=X_1+X_2+\cdots+X_{n-1}+X_n$

We want to find $\mathrm{Var}(Y)$ . By definition,

$\mathrm{Var}(Y)=\mathbb E[(Y-\mathbb E[Y])^2]=\mathbb E[Y^2]-\mathbb E[Y]^2$

As stated in the question, there is a $\dfrac1n$ probability that any one person will get off at floor $n$ (here, $n$ refers to any of the $n$ total floors, not just the top floor). Then the probability that a person will not get off at floor $n$ is $1-\dfrac1n$ . There are $m$ people in the elevator, so the probability that not a single one gets off at floor $n$ is $\left(1-\dfrac1n\right)^m$ .

So,

$\mathbb P(X_i=x)\begin{cases}\left(1-\dfrac1n\right)^m&\text{for }x=1\\\\1-\left(1-\dfrac1n\right)^m&\text{for }x=0\end{cases}$

which means

$\mathbb E[Y]=\mathbb E\left[\displaystyle\sum_{i=1}^nX_i\right]=\displaystyle\sum_{i=1}^n\mathbb E[X_i]=\sum_{i=1}^n\left(1\cdot\left(1-\dfrac1n\right)^m+0\cdot\left(1-\left(1-\dfrac1n\right)^m\right)$
$\implies\mathbb E[Y]=n\left(1-\dfrac1n\right)^m$

and

$\mathbb E[Y^2]=\mathbb E\left[\left(\displaystyle\sum_{i=1}^n{X_i}\right)^2\right]=\mathbb E\left[\displaystyle\sum_{i=1}^n{X_i}^2+2\sum_{1\le i$

Computing $\mathbb E[{X_i}^2]$ is trivial since it's the same as $\mathbb E[X_i]$ . (Do you see why?)

Next, we want to find the expected value of the following random variable, when $i\neq j$ :

$X_iX_j=\begin{cases}1&\text{if }X_i=1\text{ and }X_j=1\\0&\text{otherwise}\end{cases}$

If $X_iX_j=0$ , we don't care; when we compute $\mathbb E[X_iX_j]$ , the contributing terms will vanish. We only want to see what happens when both floors are not visited.

$\mathbb P(X_iX_j=1)=\left(1-\dfrac2n\right)^m$
$\implies\mathbb E[X_iX_j]=\left(1-\dfrac2n\right)^m$
$\implies2\displaystyle\sum_{1\le i$

where we multiply by $n(n-1)$ because that's how many ways there are of choosing indices $i,j$ for $X_iX_j$ such that $1\le i$ .

So,

$\mathrm{Var}[Y]=n\left(1-\dfrac1n\right)^m+2n(n-1)\left(1-\dfrac2n\right)^m-n^2\left(1-\dfrac1n\right)^{2m}$

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