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2 years ago

When 4 times a number is increased by 40, the answer is the same as when 100 is decreased by the number. find the number?

1 answer:

8 0

The number is x

4x+40=100-x
add x to both sides
5x+40=100
minus 40 both sides
5x=60
divide both sides by 5
x=12
the number is 12

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Let f(x,y,z) = ztan-1(y2) i + z3ln(x2 + 1) j + z k. find the flux of f across the part of the paraboloid x2 + y2 + z = 3 that li

Sophie [7]

Consider the closed region $V$ bounded simultaneously by the paraboloid and plane, jointly denoted $S$ . By the divergence theorem,

$\displaystyle\iint_S\mathbf f(x,y,z)\cdot\mathrm dS=\iiint_V\nabla\cdot\mathbf f(x,y,z)\,\mathrm dV$

And since we have

$\nabla\cdot\mathbf f(x,y,z)=1$

the volume integral will be much easier to compute. Converting to cylindrical coordinates, we have

$\displaystyle\iiint_V\nabla\cdot\mathbf f(x,y,z)\,\mathrm dV=\iiint_V\mathrm dV$
$=\displaystyle\int_{\theta=0}^{\theta=2\pi}\int_{r=0}^{r=1}\int_{z=2}^{z=3-r^2}r\,\mathrm dz\,\mathrm dr\,\mathrm d\theta$
$=\displaystyle2\pi\int_{r=0}^{r=1}r(3-r^2-2)\,\mathrm dr$
$=\dfrac\pi2$

Then the integral over the paraboloid would be the difference of the integral over the total surface and the integral over the disk. Denoting the disk by $D$ , we have

$\displaystyle\iint_{S-D}\mathbf f\cdot\mathrm dS=\frac\pi2-\iint_D\mathbf f\cdot\mathrm dS$

Parameterize $D$ by

$\mathbf s(u,v)=u\cos v\,\mathbf i+u\sin v\,\mathbf j+2\,\mathbf k$
$\implies\mathbf s_u\times\mathbf s_v=u\,\mathbf k$

which would give a unit normal vector of $\mathbf k$ . However, the divergence theorem requires that the closed surface $S$ be oriented with outward-pointing normal vectors, which means we should instead use $\mathbf s_v\times\mathbf s_u=-u\,\mathbf k$ .

Now,

$\displaystyle\iint_D\mathbf f\cdot\mathrm dS=\int_{u=0}^{u=1}\int_{v=0}^{v=2\pi}\mathbf f(x(u,v),y(u,v),z(u,v))\cdot(-u\,\mathbf k)\,\mathrm dv\,\mathrm du$
$=\displaystyle-4\pi\int_{u=0}^{u=1}u\,\mathrm du$
$=-2\pi$

So, the flux over the paraboloid alone is

$\displaystyle\iint_{S-D}\mathbf f\cdot\mathrm dS=\frac\pi2-(-2\pi)=\dfrac{5\pi}2$

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3 years ago

Enter the correct value so that each expression is a perfect-square trinomial. x2 – 10x +

Marrrta [24]

Use the formula ( $\frac{b}{2}$ )^2

in order to create a new term to complete the square.

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3 years ago

There is a group of 10 people who are ordering pizza. If each person gets 2 slices and each pizza has 4 slices, how many pizzas

Sonbull [250]

Answer:

5 pizzas

Step-by-step explanation: If you have 10 people and each will get two slices then you will need 20 pieces of pizza because 10x2 is 20. If each pizza has 4 slices then you will need 5 pizzas because 4/20 is 5.

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2 years ago

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What is the value of the n in this equation n + 16 = 21

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Answer:

n = 5

Step-by-step explanation:

Given

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2 years ago

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Students at Maple school earned $708 selling candles. They want to accumulate $2000 for a club trio. What percent of their goal

Sholpan [36]

Answer:

The correct answer is 35.4%

Step-by-step explanation:

Let's check the information provided in the question:

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Earnings for the candles selling = US$ 708

For calculating the accumulated percentage, we can do it this way:

Accumulated percentage = Earnings / Savings goal

Accumulated percentage = 708 / 2,000 * 100

Accumulated percentage = 0.354 * 100

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Students at Maple School has accumulated 35.4% of their savings goal with the candles selling.

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3 years ago