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2 years ago

Find the number of terms, n, of the arithmetic series given a1=11, an=95, and Sn=689.

Mathematics

1 answer:

borishaifa [10]2 years ago

4 0

Answer:

Step-by-step explanation:

Its calculate the common difference first.

(95-11)/(n-1).

We also have the sum of these n terms is 689.

So we have the following:

+(11+(95-11)/(n-1))

+(11+2(95-11)/(n-1))

+...

+(11+(n-1)(95-11)/(n-1))

This can be re-expressed alittle:

There are (n) amount of 11's in the addition... also 1+2+3+...+(n-1)=(n-1)(n)/2.

So we have the sum is

11(n)+n(n-1)/2×(95-11)/(n-1)

But this equal to 689.

We need to solve the following equation:

11(n)+n(n-1)/2×(95-11)/(n-1)=689

The (n-1)'s in second term can cancel.

11(n)+n/2×84=689

11n+42n=689

53n=689

n=689/53

n=13

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Answer:

Choice d.

Step-by-step explanation:

Consistent means the linear functions will have at least one solution.

Independent means the it will just that one solution.

Dependent means the system will have infinitely many solutions.

So we are looking for a pair of equations that consist of the same line.

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If m and b are the same amongst the pair, then that pair is the same line and the system is consistent and dependent.

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If m is different, then the pair will have one solution and will be consistent and independent.

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Choice A:

First line has m=1 and b=4.

Second line has m=1 and b=-4.

These lines are parallel.

This system is inconsistent.

Choice B:

First line is x+y=4 and it isn't in y=mx+b form.

Second line is 2x+2y=6 and it isn't in y=mx+b form.

These lines do have the same form though. This is actually standard form.

If you divide second equation by 2 on both sides you get: x+y=3

The lines are not the same.

We are looking for the same line.

Now we could go ahead and determine to call this system.

If x+y has value 4 then how could x+y have value 3. It is not possible. There is no solution. These lines are parallel.

Need more convincing. Let's put them into slope-intercept form.

x+y=4

Subtract x on both sides:

y=-x+4

m=-1 and b=4

x+y=3

Subtract x on both sides:

y=-x+3

m=-1 and b=3.

The system is inconsistent because they are parallel.

Choice c:

I'm going to go ahead in put them both in slope-intercept form:

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Subtract 3x on both sides:

y=-3x+3

So m=-3 and b=3

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Divide both sides by 2:

y=3x+3

So m=3 and b=3

The m's are different so this system will by consistent and independent.

Choice d:

The goal is the same. Put them in slope-intercept form.

4x-2y=6

Divide both sides by -2:

-2x+y=-3

Add 2x on both sides:

y=2x-3

m=2 and b=-3

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Divide both sides by -3:

-2x+y=-3

Add 2x on btoh sides:

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3 years ago

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Answer:

Step-by-step explanation:

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Answer:

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