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salantis [7]
3 years ago
8

Use sigma notation to represent the sum of the first seven terms of the following sequence -4,-6,-8.....

Mathematics
1 answer:
lina2011 [118]3 years ago
3 0

Answer:Answer:

\sum\left {{7} \atop {1}} \right -n(3+n)

Step-by-step explanation:

Given the sequence -4,-6,-8..., in order to get sigma notation to represent the sum of the first seven terms of the sequence, we need to first calculate the sum of the first seven terms of the sequence as shown;

The sum of an arithmetic series is expressed as S_n = \frac{n}{2}[2a+(n-1)d]

n is the number of terms

a is the first term of the sequence

d is the common difference

Given parameters

n = 7, a = -4 and d = -6-(-4) = -8-(-6) = -2

Required

Sum of the first seven terms of the sequence

S_7 = \frac{7}{2}[2(-4)+(7-1)(-2)]\\\\S_7 =  \frac{7}{2}[-8+(6)(-2)]\\\\S_7 =  \frac{7}{2}[-8-12]\\\\\\S_7 = \frac{7}{2} * -20\\\\S_7 = -70

The sum of the nth term of the sequence will be;

S_n = \frac{n}{2}[2(-4)+(n-1)(-2)]\\\\S_n = \frac{n}{2}[-8+(-2n+2)]\\\\S_n = \frac{n}{2}[-6-2n]\\\\S_n =  \frac{-6n}{2} -  \frac{2n^2}{2}\\S_n = -3n-n^2\\\\S_n = -n(3+n)

The sigma notation will be expressed as \sum\left {{7} \atop {1}} \right -n(3+n). <em>The limit ranges from 1 to 7 since we are to  find  the sum of the first seven terms of the series.</em>

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joe is in debt $250, but he's saving $30 each month. using the equation, y=30x-250, how long will it take joe to have $230?
Vsevolod [243]

Answer:

16

Step-by-step explanation:

so in this equation we have 2 variables, and we must figure out what those variables mean:

y: "y" is the total amount of money joe has after subtracting his debt from it

x: "x" is the # of months as the cost of each month(30) is placed just before this variable

as y is the total amount of money joe has we need to substitute it for 230 to figure out how long it took for joe to recieve that much money

230=30x-250

480=30x

x=16

it took joe 16 months to get $230

3 0
3 years ago
Find a polynomial, which, when added to the polynomial 5x2–3x–9, is equivalent to: x2−5x+6
Bess [88]

The required polynomial is:-4x^2-2x+15

Step-by-step explanation:

Let P be the polynomial that has to be found

Given

One polynomial = 5x^2-3x-9

Sum of both polynomials = x^2-5x+6

So,

(5x^2-3x-9) + P = x^2-5x+6\\P = x^2-5x+6 - (5x^2-3x-9)\\P = x^2-5x+6-5x^2+3x+9\\P = x^2-5x^2-5x+3x+6+9\\P = -4x^2-2x+15

Hence,

The required polynomial is:-4x^2-2x+15

Keywords: Polynomials, expressions

Learn more about polynomials at:

  • brainly.com/question/1704778
  • brainly.com/question/1695461

#LearnwithBrainly

3 0
3 years ago
Find the general solution of the differential equation and check the result by differentiation. (Use C for the constant of integ
atroni [7]

Answer: y=Ce^(^3^t^{^9}^)

Step-by-step explanation:

Beginning with the first differential equation:

\frac{dy}{dt} =27t^8y

This differential equation is denoted as a separable differential equation due to us having the ability to separate the variables. Divide both sides by 'y' to get:

\frac{1}{y} \frac{dy}{dt} =27t^8

Multiply both sides by 'dt' to get:

\frac{1}{y}dy =27t^8dt

Integrate both sides. Both sides will produce an integration constant, but I will merge them together into a single integration constant on the right side:

\int\limits {\frac{1}{y} } \, dy=\int\limits {27t^8} \, dt

ln(y)=27(\frac{1}{9} t^9)+C

ln(y)=3t^9+C

We want to cancel the natural log in order to isolate our function 'y'. We can do this by using 'e' since it is the inverse of the natural log:

e^l^n^(^y^)=e^(^3^t^{^9} ^+^C^)

y=e^(^3^t^{^9} ^+^C^)

We can take out the 'C' of the exponential using a rule of exponents. Addition in an exponent can be broken up into a product of their bases:

y=e^(^3^t^{^9}^)e^C

The term e^C is just another constant, so with impunity, I can absorb everything into a single constant:

y=Ce^(^3^t^{^9}^)

To check the answer by differentiation, you require the chain rule. Differentiating an exponential gives back the exponential, but you must multiply by the derivative of the inside. We get:

\frac{d}{dx} (y)=\frac{d}{dx}(Ce^(^3^t^{^9}^))

\frac{dy}{dx} =(Ce^(^3^t^{^9}^))*\frac{d}{dx}(3t^9)

\frac{dy}{dx} =(Ce^(^3^t^{^9}^))*27t^8

Now check if the derivative equals the right side of the original differential equation:

(Ce^(^3^t^{^9}^))*27t^8=27t^8*y(t)

Ce^(^3^t^{^9}^)*27t^8=27t^8*Ce^(^3^t^{^9}^)

QED

I unfortunately do not have enough room for your second question. It is the exact same type of differential equation as the one solved above. The only difference is the fractional exponent, which would make the problem slightly more involved. If you ask your second question again on a different problem, I'd be glad to help you solve it.

7 0
2 years ago
4.
alexandr1967 [171]

Answer:

c.6xy and -16xy

Step-by-step explanation:

the variables are the same

7 0
3 years ago
Read 2 more answers
0 ft elevation, diver is underwater at depth of 138 ft. In this area, the ocean floor has a depth of 247 ft. A rock formations r
KiRa [710]
We know that the ocean floor has a depth of 247 ft, and we also know that the diver is<span> underwater at depth of 138 ft, so its distance from the ocean floor will be:
</span>247-138=109 ft
<span>
Now, the </span>rock formations rises to a peak 171 to above the ocean floor, so to find <span>how many feet below the top of the rock formations is the diver, we are going to subtract the distance to the driver form the ocean floor from the rock formations height:
</span>171-109=62 ft
<span>
We can conclude that the diver is 62 feet </span><span>below the top of the rock formations.</span>

3 0
3 years ago
Read 2 more answers
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