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Travka [436]
3 years ago
10

Question (c)! How do I know that t^5-10t^3+5t=0? Thanks!

Mathematics
1 answer:
astra-53 [7]3 years ago
3 0
(a) By DeMoivre's theorem, we have

(\cos\theta+i\sin\theta)^5=\cos5\theta+i\sin5\theta

On the LHS, expanding yields

\cos^5\theta+5i\cos^4\theta\sin\theta-10\cos^3\theta\sin^2\theta-10i\cos^2\theta\sin^3\theta+5\cos\theta\sin^4\theta+i\sin^4\theta

Matching up real and imaginary parts, we have for (i) and (ii),


\cos5\theta=\cos^5\theta-10\cos^3\theta\sin^2\theta+5\cos\theta\sin^4\theta
\sin5\theta=5\cos^4\theta\sin\theta-10\cos^2\theta\sin^3\theta+\sin^5\theta

(b) By the definition of the tangent function,

\tan5\theta=\dfrac{\sin5\theta}{\cos5\theta}
=\dfrac{5\cos^4\theta\sin\theta-10\cos^2\theta\sin^3\theta+\sin^5\theta}{\cos^5\theta-10\cos^3\theta\sin^2\theta+5\cos\theta\sin^4\theta}

=\dfrac{5\tan\theta-10\tan^3\theta+\tan^5\theta}{1-10\tan^2\theta+5\tan^4\theta}
=\dfrac{t^5-10t^3+5t}{5t^4-10t^2+1}


(c) Setting \theta=\dfrac\pi5, we have t=\tan\dfrac\pi5 and \tan5\left(\dfrac\pi5\right)=\tan\pi=0. So

0=\dfrac{t^5-10t^3+5t}{5t^4-10t^2+1}

At the given value of t, the denominator is a non-zero number, so only the numerator can contribute to this reducing to 0.


0=t^5-10t^3+5t\implies0=t^4-10t^2+5

Remember, this is saying that

0=\tan^4\dfrac\pi5-10\tan^2\dfrac\pi5+5

If we replace \tan^2\dfrac\pi5 with a variable x, then the above means \tan^2\dfrac\pi5 is a root to the quadratic equation,

x^2-10x+5=0

Also, if \theta=\dfrac{2\pi}5, then t=\tan\dfrac{2\pi}5 and \tan5\left(\dfrac{2\pi}5\right)=\tan2\pi=0. So by a similar argument as above, we deduce that \tan^2\dfrac{2\pi}5 is also a root to the quadratic equation above.

(d) We know both roots to the quadratic above. The fundamental theorem of algebra lets us write

x^2-10x+5=\left(x-\tan^2\dfrac\pi5\right)\left(x-\tan^2\dfrac{2\pi}5\right)

Expand the RHS and match up terms of the same power. In particular, the constant terms satisfy

5=\tan^2\dfrac\pi5\tan^2\dfrac{2\pi}5\implies\tan\dfrac\pi5\tan\dfrac{2\pi}5=\pm\sqrt5

But \tanx>0 for all 0, as is the case for x=\dfrac\pi5 and x=\dfrac{2\pi}5, so we choose the positive root.
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Can you answer this pls ​
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just download MATH PAPA app, it will help you solve any hard mathematical problems, I see that your answers are there.

7 0
3 years ago
Question 9 Of 1000 randomly selected cases of lung cancer, 841 resulted in death within 10 years. Construct a 95% two-sided conf
givi [52]

Answer:

0.818335 ≤ p ≤ 0.86366

Step-by-step explanation:

Given that:

Sample size (n) = 1000

Positive lung cancer = 841

n(p) = 841, p(p) = 841/1000 = 0.841

n(1 - p) = 1000 - 841 = 159

1 - p = 0.159

95% confidence interval

For a 95% confidence interval : z = 1.96

P ± z√p(1-p) / n

0.841 ± 1.96 * √0.841(0.159) / 1000

0.841 - (1.96 * 0.0115636) = 0.818335344

0.841 + (1.96 * 0.0115636) = 0.863664656

0.818335 ≤ p ≤ 0.86366

4 0
3 years ago
Simplify: -|-15|<br><br> please answer correctly i'll give brainliest and 5-star rating.
12345 [234]

Answer:

-15

Step-by-step explanation:

<u>Definition of absolute value: </u>

<em>Distance from zero on a number line. </em>

<em />

Imagine a number line with 0 in the middle of it. Now mark the number 3 on it. Also mark the <em>opposite </em>of 3, which is -3. What is the <u>distance</u> from zero to those 2 points? it's 3.

This is exactly like saying |3| = 3 and |-3| = 3

Even if the number inside absolute value is negative, it <em><u>simplifies</u></em> to the positive of the same number.

_______________________________

So let's talk about your problem.

-|-15|

> the absolute value simplifies to 15

-|-15| = - 15

So that ends up being your answer.

-15

Hope this helps!!!!!!!

7 0
3 years ago
What is the total probability of rolling a single die twice, and having it land on 3 the
Shtirlitz [24]

Answer:

0,5*0,5=0,25

Step-by-step explanation:

assuming a die of 6 faces

25

0,5 for < 4; 0,5 for < 3

5 0
2 years ago
Abby went to the store to buy ice cream for her party. Each box costs $3. She has a coupon for 20% off her total. If Abby buys 3
ollegr [7]

Answer: 7.2$

hope it helps :)

step-by-step explanation:

Cost of each box = 3$

Cost of 3 boxes without 20% coupon = 9$

With 20% off Coupon = 9 by 100 multiplied by 20

                                     (the zero's cut with each other leaving)

                                     = 9 by 10 multiplied by 2

                                     (9 multiplied by 2 = 18)

                                     = 18 by 10

                                     (18 divided by 10 = 1.8)

                                     = the 20% of 9$ is equal to 1.8

                                        when subtracted with the total cost leaves 7.2$

4 0
3 years ago
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