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kumpel [21]
2 years ago
12

Let a1, a2, a3, ... be a sequence of positive integers in arithmetic progression with common difference

Mathematics
1 answer:
Bezzdna [24]2 years ago
3 0

Since a_1,a_2,a_3,\cdots are in arithmetic progression,

a_2 = a_1 + 2

a_3 = a_2 + 2 = a_1 + 2\cdot2

a_4 = a_3+2 = a_1+3\cdot2

\cdots \implies a_n = a_1 + 2(n-1)

and since b_1,b_2,b_3,\cdots are in geometric progression,

b_2 = 2b_1

b_3=2b_2 = 2^2 b_1

b_4=2b_3=2^3b_1

\cdots\implies b_n=2^{n-1}b_1

Recall that

\displaystyle \sum_{k=1}^n 1 = \underbrace{1+1+1+\cdots+1}_{n\,\rm times} = n

\displaystyle \sum_{k=1}^n k = 1 + 2 + 3 + \cdots + n = \frac{n(n+1)}2

It follows that

a_1 + a_2 + \cdots + a_n = \displaystyle \sum_{k=1}^n (a_1 + 2(k-1)) \\\\ ~~~~~~~~ = a_1 \sum_{k=1}^n 1 + 2 \sum_{k=1}^n (k-1) \\\\ ~~~~~~~~ = a_1 n +  n(n-1)

so the left side is

2(a_1+a_2+\cdots+a_n) = 2c n + 2n(n-1) = 2n^2 + 2(c-1)n

Also recall that

\displaystyle \sum_{k=1}^n ar^{k-1} = \frac{a(1-r^n)}{1-r}

so that the right side is

b_1 + b_2 + \cdots + b_n = \displaystyle \sum_{k=1}^n 2^{k-1}b_1 = c(2^n-1)

Solve for c.

2n^2 + 2(c-1)n = c(2^n-1) \implies c = \dfrac{2n^2 - 2n}{2^n - 2n - 1} = \dfrac{2n(n-1)}{2^n - 2n - 1}

Now, the numerator increases more slowly than the denominator, since

\dfrac{d}{dn}(2n(n-1)) = 4n - 2

\dfrac{d}{dn} (2^n-2n-1) = \ln(2)\cdot2^n - 2

and for n\ge5,

2^n > \dfrac4{\ln(2)} n \implies \ln(2)\cdot2^n - 2 > 4n - 2

This means we only need to check if the claim is true for any n\in\{1,2,3,4\}.

n=1 doesn't work, since that makes c=0.

If n=2, then

c = \dfrac{4}{2^2 - 4 - 1} = \dfrac4{-1} = -4 < 0

If n=3, then

c = \dfrac{12}{2^3 - 6 - 1} = 12

If n=4, then

c = \dfrac{24}{2^4 - 8 - 1} = \dfrac{24}7 \not\in\Bbb N

There is only one value for which the claim is true, c=12.

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A data set includes 103 body temperatures of healthy adult humans having a mean of 98.1 F and a standard deviation of 0.56 F. Co
Ira Lisetskai [31]

Answer:

The 99​% confidence interval estimate of the mean body temperature of all healthy humans is (97.955F, 98.245F).

98.6F is above the upper end of the interval, which means that the sample suggests that the mean body temperature could be lower than 98.6F.

Step-by-step explanation:

The first step is finding the confidence interval

The sample size is 103.

The first step to solve this problem is finding how many degrees of freedom there are, that is, the sample size subtracted by 1. So

df = 103-1 = 102

Then, we need to subtract one by the confidence level \alpha and divide by 2. So:

\frac{1-0.99}{2} = \frac{0.01}{2} = 0.005

Now, we need our answers from both steps above to find a value T in the t-distribution table. So, with 102 and 0.005 in the t-distribution table, we have T = 2.63.

Now, we need to find the standard deviation of the sample. That is:

s = \frac{0.56}{\sqrt{103}} = 0.055

Now, we multiply T and s

M = T*s = 2.63*0.055 = 0.145

For the lower end of the interval, we subtract the mean by M. So 98.1 - 0.145 = 97.955F.

For the upper end of the interval, we add the mean to M. So 98.1 + 0.145 = 98.245F.

The 99​% confidence interval estimate of the mean body temperature of all healthy humans is (97.955F, 98.245F).

98.6F is above the upper end of the interval, which means that the sample suggests that the mean body temperature could be lower than 98.6F.

5 0
3 years ago
Which postulate or theorem can be used to
sveticcg [70]

Answer:

AA Similarity Postulate

Step-by-step explanation:

we know that

If two figures are similar, then the ratio of its corresponding sides is proportional and its corresponding angles are congruent

step 1

Verify the proportion of the corresponding sides

\frac{PS}{PQ}=\frac{PT}{PR}

substitute

\frac{45}{20}=\frac{36}{16}

2.25=2.25 ----> is true

Corresponding sides are proportional

Triangle PQR is similar to Triangle PST

That means

Corresponding angles must be congruent

side QR is parallel side ST

and

m\angle PQR=m\angle PST ----> by corresponding angles

m\angle PRQ=m\angle PTS --> by corresponding angles

so

PQR is similar to PST by AA Similarity Postulate

4 0
3 years ago
Add the polynomials: (-5 - 7x^2); (5 + 7x^3) *
cestrela7 [59]

Answer:

- 7 {x}^{2}  + 7 {x}^{3}

Step-by-step explanation:

( - 5 - 7 {x}^{2} ) + (5 + 7 {x}^{3} ) \\  =  - 5 - 7 {x}^{2}  + 5 + 7 {x}^{3}  \\  = - 7 {x}^{2}  + 7 {x}^{3}

3 0
3 years ago
ιғ a cιrcle нaѕ a radιυѕ oғ 12 cм and a ѕecтor deғιned вy a 120 degree arc, wнaт ιѕ тнe area oғ тнe ѕecтor
dolphi86 [110]
120
times 12 - 360
it should give you the right answer if you solve the problem like that

5 0
3 years ago
Find the slope of the line passing through the points (8,-6) <br> and (4,-8)<br> .
Murljashka [212]

Answer:

1/2 is the slope of the line

Step-by-step explanation:

To find slope, use the following equation

slope (m) = (y₂ - y₁)/(x₂ - x₁)

First, set each coordinate. Let:

(x₁ , y₁) = (8 , -6)

(x₂ , y₂) = (4 , -8)

Plug in the corresponding numbers for the corresponding variables.

m = (y₂ - y₁)/(x₂ - x₁)

m = (-8 - (-6))/(4 - 8)

Simplify. Note that two negative signs would result in a positive sign.

m = (-8 + 6)/(4 - 8)

Combine like terms.

m = -2/-4

Simplify. Divide common factors from both the numerator and denominator.

m = (-2/-4)/(-2/-2) = 1/2

1/2 is the slope of the line

~

4 0
3 years ago
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