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3 years ago

Solve the equation. x² + 6x+15=0

Mathematics

1 answer:

lara [203]3 years ago

3 0

Answer:

x = -3 + i√6 and x = -3 - i√6

Step-by-step explanation:

Let's apply the "completing the square" method to find the roots of this equation.

Take half of the coefficient 6 of x, square it and add this result to x^2 + 6x. Then subtract the same quantity:

x^2 + 6x + 15 becomes

x^2 + 6x + 3^2 - 3^2 + 15 = 0

Rewriting the first three terms as the square of a binomial, we ge:

(x + 3)^2 - 9 + 15 = 0, which simplifies to:

(x + 3)^2 + 6 = 0, or (x + 3)^2 = -6

Taking the square root of both sides:

x + 3 = ±i√6

Then the two roots are complex:

x = -3 + i√6 and x = -3 - i√6

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The Department of Agriculture is monitoring the spread of mice by placing 100 mice at the start of the project. The population,

uranmaximum [27]

Answer:

Step-by-step explanation:

Assuming that the differential equation is

$\frac{dP}{dt} = 0.04P\left(1-\frac{P}{500}\right)$ .

We need to solve it and obtain an expression for $P(t)$ in order to complete the exercise.

First of all, this is an example of the logistic equation, which has the general form

$\frac{dP}{dt} = kP\left(1-\frac{P}{K}\right)$ .

In order to make the calculation easier we are going to solve the general equation, and later substitute the values of the constants, notice that $k=0.04$ and $K=500$ and the initial condition $P(0)=100$ .

Notice that this equation is separable, then

$\frac{dP}{P(1-P/K)} = kdt$ .

Now, intagrating in both sides of the equation

$\int\frac{dP}{P(1-P/K)} = \int kdt = kt +C$ .

In order to calculate the integral in the left hand side we make a partial fraction decomposition:

$\frac{1}{P(1-P/K)} = \frac{1}{P} - \frac{1}{K-P}$ .

So,

$\int\frac{dP}{P(1-P/K)} = \ln|P| - \ln|K-P| = \ln\left| \frac{P}{K-P} \right| = -\ln\left| \frac{K-P}{P} \right|$ .

We have obtained that:

$-\ln\left| \frac{K-P}{P}\right| = kt +C$

which is equivalent to

$\ln\left| \frac{K-P}{P}\right|= -kt -C$

Taking exponentials in both hands:

$\left| \frac{K-P}{P}\right| = e^{-kt -C}$

Hence,

$\frac{K-P(t)}{P(t)} = Ae^{-kt}$ .

The next step is to substitute the given values in the statement of the problem:

$\frac{500-P(t)}{P(t)} = Ae^{-0.04t}$ .

We calculate the value of $A$ using the initial condition $P(0)=100$ , substituting $t=0$ :

$\frac{500-100}{100} = A}$ and $A=4$ .

So,

$\frac{500-P(t)}{P(t)} = 4e^{-0.04t}$ .

Finally, as we want the value of $t$ such that $P(t)=200$ , we substitute this last value into the above equation. Thus,

$\frac{500-200}{200} = 4e^{-0.04t}$ .

This is equivalent to $\frac{3}{8} = e^{-0.04t}$ . Taking logarithms we get $\ln\frac{3}{8} = -0.04t$ . Then,

$t = \frac{\ln\frac{3}{8}}{-0.04} \approx 24.520731325$ .

So, the population of rats will be 200 after 25 months.

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3 years ago

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ikadub [295]

The answer is D.

Have a great day!

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2 years ago

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belka [17]

Answer:

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Step-by-step explanation:

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8 0

2 years ago

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You invest AED 5000 in a saving account that earns 4% interest each year. If you do not use the account for a year, how much mon

Viktor [21]

Answer:

5200 AED or 1404 USD

Step-by-step explanation:

You have 5000 in your account. If your money grows 4% each year, it's basically like multiplying by 1.04.

5000 * 1.04 = 5200

If the question is asking in USD, the conversion rate from AED to USD is

AED * 0.27 = USD

We can substitute

5200 AED* 0.27 = 1404 USD.

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2 years ago

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zhuklara [117]

Answer:

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Step-by-step explanation:

if sin²2x=1-cos²2x, then

1-cos²2x-2cos2x+2=0; ⇒ cos²2x+2cos2x-3=0; ⇔ (cos2x+3)(cos2x-1)=0;

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2 years ago