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3 years ago

Question 10 of 10

Mathematics

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Reil [10]3 years ago

4 0

please help me out please help me out please help me out

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Determine the formula for the nth term of the sequence:<br>-2,1,7,25,79,...

rodikova [14]

A plausible guess might be that the sequence is formed by a degree-4* polynomial,

$x_n = a n^4 + b n^3 + c n^2 + d n + e$

From the given known values of the sequence, we have

$\begin{cases}a+b+c+d+e = -2 \\ 16 a + 8 b + 4 c + 2 d + e = 1 \\ 81 a + 27 b + 9 c + 3 d + e = 7 \\ 256 a + 64 b + 16 c + 4 d + e = 25 \\ 625 a + 125 b + 25 c + 5 d + e = 79\end{cases}$

Solving the system yields coefficients

$a=\dfrac58, b=-\dfrac{19}4, c=\dfrac{115}8, d = -\dfrac{65}4, e=4$

so that the n-th term in the sequence might be

$\displaystyle x_n = \boxed{\frac{5 n^4}{8}-\frac{19 n^3}{4}+\frac{115 n^2}{8}-\frac{65 n}{4}+4}$

Then the next few terms in the sequence could very well be

$\{-2, 1, 7, 25, 79, 208, 466, 922, 1660, 2779, \ldots\}$

It would be much easier to confirm this had the given sequence provided just one more term...

* Why degree-4? This rests on the assumption that the higher-order forward differences of $\{x_n\}$ eventually form a constant sequence. But we only have enough information to find one term in the sequence of 4th-order differences. Denote the k-th-order forward differences of $\{x_n\}$ by $\Delta^{k}\{x_n\}$ . Then

• 1st-order differences:

$\Delta\{x_n\} = \{1-(-2), 7-1, 25-7, 79-25,\ldots\} = \{3,6,18,54,\ldots\}$

• 2nd-order differences:

$\Delta^2\{x_n\} = \{6-3,18-6,54-18,\ldots\} = \{3,12,36,\ldots\}$

• 3rd-order differences:

$\Delta^3\{x_n\} = \{12-3, 36-12,\ldots\} = \{9,24,\ldots\}$

• 4th-order differences:

$\Delta^4\{x_n\} = \{24-9,\ldots\} = \{15,\ldots\}$

From here I made the assumption that $\Delta^4\{x_n\}$ is the constant sequence {15, 15, 15, …}. This implies $\Delta^3\{x_n\}$ forms an arithmetic/linear sequence, which implies $\Delta^2\{x_n\}$ forms a quadratic sequence, and so on up $\{x_n\}$ forming a quartic sequence. Then we can use the method of undetermined coefficients to find it.

5 0

2 years ago

Solve by substitution 9x+y=21, -x-3=y

VashaNatasha [74]

Answer:

point form: $(3,-6)$

equation form: $x=3, y=-6$

Step-by-step explanation:

4 0

2 years ago

The volume of a rectangular prism is 50 5/8 cubic inches.

Temka [501]

mcyt mcyt mcyt mcyt mcyt

6 0

2 years ago

Evaluate the function f(x) at the given numbers (correct to six decimal places). F(x) = x2 − 5x x2 − x − 20 , x = 5.5, 5.1, 5.05

exis [7]

we are given

$f(x)=\frac{x^2-5x}{x^2-x-20}$

Firstly, we will simplify it

$f(x)=\frac{x(x-5)}{(x-5)(x+4)}$

$f(x)=\frac{x}{(x+4)}$

At x=5.5:

we can plug x=5.5

$f(5.5)=\frac{5.5}{(5.5+4)}$

$f(5.5)=0.578947$

At x=5.1:

we can plug x=5.1

$f(5.1)=\frac{5.1}{(5.1+4)}$

$f(5.1)=0.56043956$

At x=5.05:

we can plug x=5.05

$f(5.05)=\frac{5.05}{(5.05+4)}$

$f(5.05)=0.558011$

At x=5.01:

we can plug x=5.01

$f(5.01)=\frac{5.01}{(5.01+4)}$

$f(5.01)=0.5560488$

At x=5.005:

we can plug x=5.005

$f(5.005)=\frac{5.005}{(5.005+4)}$

$f(5.005)=0.5558023$

At x=5.001:

we can plug x=5.001

$f(5.001)=\frac{5.001}{(5.001+4)}$

$f(5.001)=0.5556049$

At x=4.9:

we can plug x=4.9

$f(4.9)=\frac{4.9}{(4.9+4)}$

$f(4.9)=0.5505617$

At x=4.95:

we can plug x=4.95

$f(4.95)=\frac{4.95}{(4.95+4)}$

$f(4.95)=0.5530726$

At x=4.99:

we can plug x=4.99

$f(4.99)=\frac{4.99}{(4.99+4)}$

$f(4.99)=0.55506117$

At x=4.995:

we can plug x=4.995

$f(4.995)=\frac{4.995}{(4.995+4)}$

$f(4.995)=0.55503085$

At x=4.999:

we can plug x=4.999

$f(4.999)=\frac{4.999}{(4.999+4)}$

$f(4.999)=0.55550616$

7 0

3 years ago

6. A sector of a circle is a region bound by an arc and the two radii that share the arc's endpoints. Suppose you have a dartboa

Aliun [14]

Given the dartboard of diameter $20in$ , divided into 20 congruent sectors,

The central angle is $18^\circ$

The fraction of a circle taken up by one sector is $\frac{1}{20}$

The area of one sector is $15.7in^2$ to the nearest tenth

The area of a circle is given by the formula

$A=\pi r^2$

A sector of a circle is a fraction of a circle. The fraction is given by $\frac{\theta}{360^\circ}$ . Where $\theta$ is the angle subtended by the sector at the center of the circle.

The formula for computing the area of a sector, given the angle at the center is

$A_s=\dfrac{\theta}{360^\circ}\times \pi r^2$

<h3>Given information</h3>

We given a circle (the dartboard) with diameter of $20in$ , divided into 20 equal(or, congruent) sectors

<h3>Part I: Finding the central angle</h3>

To find the central angle, divide $360^\circ$ by the number of sectors. Let $\alpha$ denote the central angle, then

$\alpha=\dfrac{360^\circ}{20}\\\\\alpha=18^\circ$

<h3>Part II: Find the fraction of the circle that one sector takes</h3>

The fraction of the circle that one sector takes up is found by dividing the angle a sector takes up by $360^\circ$ . The angle has already been computed in Part I (the central angle, $\alpha$ ). The fraction is

$f=\dfrac{\alpha}{360^\circ}\\\\f=\dfrac{18^\circ}{360^\circ}=\dfrac{1}{20}$

<h3>Part III: Find the area of one sector to the nearest tenth</h3>

The area of one sector can be gotten by multiplying the fraction gotten from Part II, with the area formula. That is

$A_s=f\times \pi r^2\\=\dfrac{1}{20}\times3.14\times\left(\dfrac{20}{2}\right)^2\\\\=\dfrac{1}{20}\times3.14\times10^2=15.7in^2$

Learn more about sectors of a circle brainly.com/question/3432053

8 0

2 years ago