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4 years ago

Find S9 for the geometric sequence: an=2∙5n−2 Please show work

Mathematics

1 answer:

Anika [276]4 years ago

8 0

Answer:

I guess that the geometric sequence is:

An = 2*5^(n - 2)

we usually have that that a geometric sequence is something like:

A*r^n.

so i will write the first two terms of our sequence separated, and i will calculate the summation of the first seven terms after n = 2.

A0 = 2*5^(-2) = 2/25

A1 = 2*5^-1 = 2/5

Then, the sum for a geometric sequence is:

SN = A(1 - r^N)/(1 - r)

in this case, A = 2 and r = 5, and i will use N = 7 for the sequence 2*5^n

S7 = 2*(1 - 5^7)/(1 - 5) = 39,062.

now we add the first terms that we obtained before and get:

S9 = 2/25 + 2/5 + 39,062 = 39,062.48

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Identify the vertex and the y-intercept of the graph of each function. Show your work

olga2289 [7]

vertex
y = 3(x - 2)² - 4
y = 3((x - 2)(x - 2)) - 4
y = 3(x² - 2x - 2x + 4) - 4
y = 3(x² - 4x + 4) - 4
y = 3(x²) - 3(4x) + 3(4) - 4
y = 3x² - 12x + 12 - 4
y = 3x² - 12x + 8
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x = 12 +/- √(144 - 96)
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x = 12 +/- √(48)
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x = 12 +/- 6.93
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x = 2 +/- 1.155
x = 2 + 1.155 x = 2 - 1.155
x = 3.155 x = 0.845
y = 3x² - 12x + 8
y = 3(3.155)² - 12(3.155) + 8
y = 3(1.334025) - 3.786 + 8
y = 4.002075 - 3.786 + 8
y = 0.216075 + 8
y = 8.216075
(x, y) = (3.155, 8.216075)
or
y = 3x² - 12x + 8
y = 3(0.845)² - 12(0.845) + 8
y = 3(0.714025) - 10.14 + 8
y = 2.142075 - 10.14 + 8
y = -7.857925 + 8
y = 0.142675
(x, y) = (0.845, 0.142675)
y-intercept
y = 3x² - 12x + 8
y = 3(0)² - 12(0) + 8
y = 3(0) - 0 + 8
y = 0 - 0 + 8
y = 0 + 8
0 = -y + 8
y = 8
(x, y) = (0, 8)
-------------------------------------------------------------------------------------------
vertex
y = 4(x - 5)² = 1
y = 4(x - 5)² - 1
y = 4((x - 5)(x - 5)) - 1
y = 4(x² - 5x - 5x + 25) - 1
y = 4(x² - 10x + 25) - 1
y = 4(x²) - 4(10x) + 4(25) - 1
y = 4x² - 40x + 100 - 1
y = 4x² - 40x + 99
4x² - 40x + 99 = 0
x = -(-40) +/- √((-40)² - 4(4)(99))
 2(4)
x = 40 +/- √(1600 - 1584)
 8
x = 40 +/- √(16)
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x = 40 +/- 4
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x = 5 +/- 1/2
x = 5 + 1/2 x = 5 - 1/2
x = 5 1/2 x = 4 1/2
y = 4x² - 40x + 99
y = 4(5 1/2)² - 40(5 1/2) + 99
y = 4(30 1/4) - 220 + 99
y = 121 - 220 + 99
y = -99 + 99
y = 0
(x, y) = (5 1/2, 0)
or
y = 4x² - 40x + 99
y = 4(4 1/2)² - 40(4 1/2) + 99
y = 4(20 1/4) - 180 + 99
y = 81 - 180 + 99
y = -99 + 99
y = 0
(x, y) = (4 1/2, 0)
y-intercept
y = 4x² - 40x + 99
y = 4(0)² - 40(0) + 99
y = 4(0) - 0 + 99
y = 0 - 0 + 99
y = 0 + 99
y = 99
(x, y) = (0, 99)
--------------------------------------------------------------------------------------------
vertex
y = (x - 1)² = 2
y = (x - 1)² - 2
y = ((x - 1)(x - 1)) - 2
y = (x² - x - x + 1) - 2
y = x² - 2x + 1 - 2
y = x² - 2x - 1
x² - 2x - 1 = 0
x = -(-2) +/- √((-2)² - 4(1)(-1))
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x = 2 +/- √(4 + 4)
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x = 2 +/- √(8)
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x = 2 +/- 2.83
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x = 1 +/- 1.415
x = 1 + 1.415 x = 1 - 1.415
x = 2.415 x = 0.415
y = x² - 2x - 1
y = (2.145)² - 2(2.145) - 1
y = 4.60125 - 4.029 - 1
y = 0.57225 - 1
y = 0.42775
(x, y) = (2.415, 0.42775)
or
y = x² - 2x - 1
y = (0.415)² - 2(0.415) - 1
y = 0.172225 - 0.83 - 1
y = -0.657775 - 1
y = -1.657775
(x, y) = (0.415, -1.657775)
y-intercept
y = x² - 2x - 1
y = (0)² - 2(0) - 1
y = 0 - 0 - 1
y = 0 - 1
y = -1
(x, y) = (0, -1)

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Step-by-step explanation:

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The equation

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