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3 years ago

Is 8.4 an irrational number?

Mathematics

2 answers:

OleMash [197]3 years ago

6 0

Yes because an irrational number is a number that cannot be written as a simple fraction

zhannawk [14.2K]3 years ago

3 0

No because it is a terminating decimal

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Which of the following is not one of the 8th roots of unity?

Anika [276]

Answer:

1+i

Step-by-step explanation:

To find the 8th roots of unity, you have to find the trigonometric form of unity.

1. Since $z=1=1+0\cdot i,$ then

$Rez=1,\\ \\Im z=0$

and

$|z|=\sqrt{1^2+0^2}=1,\\ \\\\\cos\varphi =\dfrac{Rez}{|z|}=\dfrac{1}{1}=1,\\ \\\sin\varphi =\dfrac{Imz}{|z|}=\dfrac{0}{1}=0.$

This gives you $\varphi=0.$

Thus,

$z=1\cdot(\cos 0+i\sin 0).$

2. The 8th roots can be calculated using following formula:

$\sqrt[8]{z}=\{\sqrt[8]{|z|} (\cos\dfrac{\varphi+2\pi k}{8}+i\sin \dfrac{\varphi+2\pi k}{8}), k=0,\ 1,\dots,7\}.$

Now

at k=0, $z_0=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 0}{8}+i\sin \dfrac{0+2\pi \cdot 0}{8})=1\cdot (1+0\cdot i)=1;$

at k=1, $z_1=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 1}{8}+i\sin \dfrac{0+2\pi \cdot 1}{8})=1\cdot (\dfrac{\sqrt{2}}{2}+i\dfrac{\sqrt{2}}{2})=\dfrac{\sqrt{2}}{2}+i\dfrac{\sqrt{2}}{2};$

at k=2, $z_2=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 2}{8}+i\sin \dfrac{0+2\pi \cdot 2}{8})=1\cdot (0+1\cdot i)=i;$

at k=3, $z_3=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 3}{8}+i\sin \dfrac{0+2\pi \cdot 3}{8})=1\cdot (-\dfrac{\sqrt{2}}{2}+i\dfrac{\sqrt{2}}{2})=-\dfrac{\sqrt{2}}{2}+i\dfrac{\sqrt{2}}{2};$

at k=4, $z_4=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 4}{8}+i\sin \dfrac{0+2\pi \cdot 4}{8})=1\cdot (-1+0\cdot i)=-1;$

at k=5, $z_5=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 5}{8}+i\sin \dfrac{0+2\pi \cdot 5}{8})=1\cdot (-\dfrac{\sqrt{2}}{2}-i\dfrac{\sqrt{2}}{2})=-\dfrac{\sqrt{2}}{2}-i\dfrac{\sqrt{2}}{2};$

at k=6, $z_6=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 6}{8}+i\sin \dfrac{0+2\pi \cdot 6}{8})=1\cdot (0-1\cdot i)=-i;$

at k=7, $z_7=\sqrt[8]{1} (\cos\dfrac{0+2\pi \cdot 7}{8}+i\sin \dfrac{0+2\pi \cdot 7}{8})=1\cdot (\dfrac{\sqrt{2}}{2}-i\dfrac{\sqrt{2}}{2})=\dfrac{\sqrt{2}}{2}-i\dfrac{\sqrt{2}}{2};$

The 8th roots are

$\{1,\ \dfrac{\sqrt{2}}{2}+i\dfrac{\sqrt{2}}{2},\ i, -\dfrac{\sqrt{2}}{2}+i\dfrac{\sqrt{2}}{2},\ -1, -\dfrac{\sqrt{2}}{2}-i\dfrac{\sqrt{2}}{2},\ -i,\ \dfrac{\sqrt{2}}{2}-i\dfrac{\sqrt{2}}{2}\}.$

Option C is icncorrect.

5 0

3 years ago

Sneha is planning a 5-night vacation. It will cost $50 for transportation, $290 for food, and $95 per night for a hotel room. Sh

Goshia [24]

Answer:

Step-by-step explanation:

Total cost for trip = 290 + 50 + 95*5 =290+50+ 475 = $ 815

Savings = $143

Money needed = 815 - 143 = $ 672

No. of driveways = 672/48 = 14

14 driveways must she shovel to have enough money to pay for the trip.

6 0

3 years ago

Question 5<br> Find the sum of the following geometric series.<br> 8+1.6+0.32+0.064 + ...

boyakko [2]

good morning,

Answer:

10×(1-0.2ⁿ)

Step-by-step explanation:

1.6/8=0.2

0.32/1.6=0.2

0.064/0.32=0.2

let S represent the sum of n term then S=8×[(1-0.2ⁿ)/(1-0.2)] = 10×(1-0.2ⁿ).

5 0

3 years ago

Please answer correctly !!!!! Will mark Brianliest !!!!!!!!!!!!!!

Irina18 [472]

Answer:

x = 97.6

Step-by-step explanation:

cos = adjacent over hypotenuse

$cos(55)=\frac{56}{x}$

* multiply each side by x *

$cos(55)*x=xcos(55)\\\frac{56}{x} *x=56\\56=xcos(55)$

* divide each side by cos ( 55 ) *

$\frac{xcos(55)}{cos(55)} =x\\\frac{56}{cos(55)} =97.63302055$

we're left with x = 97.63302055

Our last step is to round to the nearest tenth of a foot

We get that x = 97.6

4 0

3 years ago

Solve for x.<br> -5/6x-1/9x=-102<br> x = ______?

kifflom [539]

Answer:x=1/108 is your answer

-5/6x-1/9x=-102

1/x(-5/6-1/9)=-102

1/x=-102/(-17/18)=-102×-18/17=108

x=1/108

3 0

3 years ago

Read 2 more answers