Find the value of the expression |2x−8| where x=−2.5; 0; 4; 5; 9.5.

1 answer:

5 0

The absolute value $|x|$ returns the "positive version" of a number. In other words, if $x$ is already positive, then $|x|=x$ . Otherwise, if $x$ is negative, then the absolute value changes its sign, so that it returns positive: $|x|=-x$ .

So, in this case, we have to plug the required values for $x$ in the expression $2x-8$ . Then, if the result is positive we're ok, otherwise we discard the negative sign.

We have:

$x=-2.5 \implies |2x-8| = |-5-8|=|-13|=13$

$x=0 \implies |2x-8| = |0-8|=|-8|=8$

$x=4 \implies |2x-8| = |8-8|=|0|=0$

$x=5 \implies |2x-8| = |10-8|=|2|=2$

$x=9.5 \implies |2x-8| = |19-8|=|11|=11$

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A swimming pool is being drained so it can be cleaned. The amount of water in the pool is changing according to the función f(t)

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Answer:

0 ≤ t ≤ 5.

Step-by-step explanation:

In the function $f(t)$ , $t$ is the independent variable. The domain of $f$ is the set of all values of $t$ that this function can accept.

In this case, $f(t)$ is defined in a real-life context. Hence, consider the real-life constraints on the two variables. Both time and volume should be non-negative. In other words,

$t \ge 0$ .
$f(t) \ge 0$ .

The first condition is an inequality about $t$ , which is indeed the independent variable.

However, the second condition is about $f$ , the dependent variable of this function. It has to be rewritten as a condition about $t$ .

$\begin{aligned} f(t) &\ge 0 &&\text{Assumption} \cr 80000 - 16000\, t& \ge 0 && \text{Definition of} ~ f \cr 80000 & \ge 16000\, t && \begin{aligned}&\text{Add $16000\, t$} \\[-0.5em] & \text{to both sides of the inequality}\end{aligned} \cr 5 &\ge t &&\begin{aligned}&\text{Divide both sides of} \\[-0.5em] & \text{the inequality by $16000$}\end{aligned} \cr t &\le 5 && \text{Flip the inequality}\end{aligned}$ .