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4 years ago

Forty more than twice malia's age is 64

Mathematics

2 answers:

gladu [14]4 years ago

7 0

You subtract 40 from 64 and get 24. Divide 24 by 2 and your answer is 12.

Tanzania [10]4 years ago

4 0

To solve this multiply 64 times 2 to get 128. Next, add 40 and you will get 168 as your answer.

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Determine whether the integral converges.

Kryger [21]

You have one mistake which occurs when you integrate $\dfrac1{1-p^2}$ . The antiderivative of this is not in terms of $\tan^{-1}p$ . Instead, letting $p=\sin r$ (or $\cos r$ , if you want to bother with more signs) gives $\mathrm dp=\cos r\,\mathrm dr$ , making the indefinite integral equality

$\displaystyle-\frac12\int\frac{\mathrm dp}{1-p^2}=-\frac12\int\frac{\cos r}{1-\sin^2r}\,\mathrm dr=-\frac12\int\sec r\,\mathrm dr=\ln|\sec r+\tan r|+C$

and then compute the definite integral from there.

$-\dfrac12\ln|\sec r+\tan r|\stackrel{r=\sin^{-1}p}=-\dfrac12\ln\left|\dfrac{1+p}{\sqrt{1-p^2}}=\ln\left|\sqrt{\dfrac{1+p}{1-p}}\right|$
$\stackrel{p=u/2}=-\dfrac12\ln\left|\sqrt{\dfrac{1+\frac u2}{1-\frac u2}}\right|=-\dfrac12\ln\left|\sqrt{\dfrac{2+u}{2-u}}\right|$
$\stackrel{u=x+1}=-\dfrac12\ln\left|\sqrt{\dfrac{3+x}{1-x}}\right|$
$\implies-\dfrac12\displaystyle\lim_{t\to\infty}\ln\left|\sqrt{\dfrac{3+x}{1-x}}\right|\bigg|_{x=2}^{x=t}=-\frac12\left(\ln|-1|-\ln\left|\sqrt{\frac5{-1}}\right|\right)=\dfrac{\ln\sqrt5}2=\dfrac{\ln5}4$

Or, starting from the beginning, you could also have found it slightly more convenient to combine the substitutions in one fell swoop by letting $x+1=2\sec y$ . Then $\mathrm dx=2\sec y\tan y\,\mathrm dy$ , and the integral becomes

$\displaystyle\int_2^\infty\frac{\mathrm dx}{(x+1)^2-4}=\int_{\sec^{-1}(3/2)}^{\pi/2}\frac{2\sec y\tan y}{4\sec^2y-4}\,\mathrm dy$
$\displaystyle=\frac12\int_{\sec^{-1}(3/2)}^{\pi/2}\csc y\,\mathrm dy$
$\displaystyle=-\frac12\ln|\csc y+\cot y|\bigg|_{y=\sec^{-1}(3/2}}^{y=\pi/2}$
$\displaystyle=-\frac12\lim_{t\to\pi/2^-}\ln|\csc y+\cot y|\bigg|_{y=\sec^{-1}(3/2)}^{y=t}$
$\displaystyle=-\frac12\left(\lim_{t\to\pi/2^-}\ln|\csc t+\cot t|-\ln\frac5{\sqrt5}\right)$
$=\dfrac{\ln\sqrt5}2-\dfrac{\ln|1|}2$
$=\dfrac{\ln5}4$

Another way to do this is to notice that the integrand's denominator can be factorized.

$x^2+2x-3=(x+3)(x-1)$

So,

$\dfrac1{x^2+2x-3}=\dfrac1{(x+3)(x-1)}=\dfrac14\left(\dfrac1{x-1}-\dfrac1{x+3}\right)$

There are no discontinuities to worry about since you're integrate over $[2,\infty)$ , so you can proceed with integrating straightaway.

$\displaystyle\int_2^\infty\frac{\mathrm dx}{x^2+2x-3}=\frac14\lim_{t\to\infty}\int_2^t\left(\frac1{x-1}-\frac1{x+3}\right)\,\mathrm dx$
$=\displaystyle\frac14\lim_{t\to\infty}(\ln|x-1|-\ln|x+3|)\bigg|_{x=2}^{x=t}$
$=\displaystyle\frac14\lim_{t\to\infty}\ln\left|\frac{x-1}{x+3}\right|\bigg|_{x=2}^{x=t}$
$=\displaystyle\frac14\left(\lim_{t\to\infty}\ln\left|\frac{t-1}{t+3}\right|-\ln\frac15\right)$
$=\displaystyle\frac14\left(\ln1-\ln\frac15\right)$
$=-\dfrac14\ln\dfrac15=\dfrac{\ln5}4$

Just goes to show there's often more than one way to skin a cat...

7 0

3 years ago

(4x – 6) + (5x + 1).

juin [17]

Answer:

9x - 5

Step-by-step explanation:

(4x – 6) + (5x + 1).

4x - 6 + 5x +1

9x - 5

Have a good day

7 0

3 years ago

Read 2 more answers

Im not sure if anyone can help me but if you can i would really appreciate it cuz im really confused about this so thank you. al

Advocard [28]

Answer:

Question 1) 6x+5

Question 2) Blank #1: sum. Blank #2: 5. Blank #3: 4

See work in the attachment. If you're still confused, read the step-by-step explanation for a more in-depth explanation of what exactly I did for my work. Let me know if you have any questions :>

Step-by-step explanation:

For question 1, it's important to know that the perimeter is equal to the sum of all the sides. Since the shape is a rectangle, the sides opposite of each other are the same length. Thus, the left and right sides are both 3x - 3. 2(3x - 3) = 6x - 6. The unknown value, which I called a, is the same for both the top and the bottom. To find it, you must first subtract 6x - 6 from the perimeter of 18x + 4. This equals 12x + 10. Then, divide that answer by 2 to get the unknown side. You then get 6x + 5 as the answer for the unknown side.

To make sure it's correct, you can plug in a random number for x. In this case, I checked my work by plugging 2 in for x.

Perimeter = 18(2) + 4 = 36 + 4 = 40

Perimeter = 6(2) + 5 + 6(2) + 5 + 3(2) - 3 + 3(2) - 3 = 12 + 5 + 12 + 5 + 6 - 3 + 6 - 3 = 24 + 10 + 12 - 6 = 40

For question 2, the main idea you need to know is that A = lw. The area of the first rectangle is 6 * 5 = 30. The area of the second rectangle is 6 * 4 = 24. When you add them together, you get 54. The area of the rectangle that is formed when you combine rectangle 1 and rectangle 2 is 6 * 9 = 54. This shows that 6(4) + 6(5) = 6(9)