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3 years ago

Solve x2 + 6x = 7 by completing the square. What is the solution set of the equation?

Mathematics

1 answer:

Vikentia [17]3 years ago

4 0

$x^2+6x=7$
$x^2+6x+9=7+9$
$(x+3)^2=16$
$(x+3)^2=4^2$
$x+3=4\lor x+3=-4$
$x=4-3\lor x=-4-3$
$\boxed{x=1\lor x=-7}$

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Suppose that \nabla f(x,y,z) = 2xyze^{x^2}\mathbf{i} + ze^{x^2}\mathbf{j} + ye^{x^2}\mathbf{k}. if f(0,0,0) = 2, find f(1,1,1).

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The simplest path from (0, 0, 0) to (1, 1, 1) is a straight line, denoted $C$ , which we can parameterize by the vector-valued function,

$\mathbf r(t)=(1-t)(\mathbf i+\mathbf j+\mathbf k)$

for $0\le t\le1$ , which has differential

$\mathrm d\mathbf r=-(\mathbf i+\mathbf j+\mathbf k)\,\mathrm dt$

Then with $x(t)=y(t)=z(t)=1-t$ , we have

$\displaystyle\int_{\mathcal C}\nabla f(x,y,z)\cdot\mathrm d\mathbf r=\int_{t=0}^{t=1}\nabla f(x(t),y(t),z(t))\cdot\mathrm d\mathbf r$

$=\displaystyle\int_{t=0}^{t=1}\left(2(1-t)^3e^{(1-t)^2}\,\mathbf i+(1-t)e^{(1-t)^2}\,\mathbf j+(1-t)e^{(1-t)^2}\,\mathbf k\right)\cdot-(\mathbf i+\mathbf j+\mathbf k)\,\mathrm dt$

$\displaystyle=-2\int_{t=0}^{t=1}e^{(1-t)^2}(1-t)(t^2-2t+2)\,\mathrm dt$

Complete the square in the quadratic term of the integrand: $t^2-2t+2=(t-1)^2+1=(1-t)^2+1$ , then in the integral we substitute $u=1-t$ :

$\displaystyle=-2\int_{t=0}^{t=1}e^{(1-t)^2}(1-t)((1-t)^2+1)\,\mathrm dt$

$\displaystyle=-2\int_{u=0}^{u=1}e^{u^2}u(u^2+1)\,\mathrm du$

Make another substitution of $v=u^2$ :

$\displaystyle=-\int_{v=0}^{v=1}e^v(v+1)\,\mathrm dv$

Integrate by parts, taking

$r=v+1\implies\mathrm dr=\mathrm dv$

$\mathrm ds=e^v\,\mathrm dv\implies s=e^v$

$\displaystyle=-e^v(v+1)\bigg|_{v=0}^{v=1}+\int_{v=0}^{v=1}e^v\,\mathrm dv$

$\displaystyle=-(2e-1)+(e-1)=-e$

So, we have by the fundamental theorem of calculus that

$\displaystyle\int_C\nabla f(x,y,z)\cdot\mathrm d\mathbf r=f(1,1,1)-f(0,0,0)$

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3 years ago

A national survey indicated that 30% of adults conduct their banking online. It also found that 40% are under the age of 50. and

Svet_ta [14]

Answer:

Step-by-step explanation:

Hello!

I'll express all the given percentages as probabilities:

Given the events:

Banking online (Bo)

Under the age of 50 (<50)

P(Bo)= 0.30

P(<50)= 0.40

P(Bo ∩ <50)= 0.25

1) What percentage of adults do not conduct their banking online?

The event "adults that do not conduct their baking online" is the complement of the event "adults that conduct their baking online" Symbolically $Bo^c$

P( $Bo^c$ )= 1 - P(Bo)= 1 - 0.30 = 0.70

2) What type of probability is 25%?

The probability P(Bo ∩ <50)= 0.25 is a joint probability, it indicates the intersection between both events.

3) Construct a contingency table showing all joint and marginal probabilities.

Check attachment.

4) What is the probability that an individual conducts banking online given that the individual is under the age of 50?

Symbolically:

P(Bo/<50)= <u> P(Bo ∩ <50) </u> = <u> 0.25 </u> = 0.625

P(<50) 0.40

I hope it helps!

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3 years ago