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Calculate the Harmonic Imply


The harmonic imply (H) of n numbers ( x1, x2, x3, … , xn ), additionally referred to as subcontrary imply, is given by the components beneath.

Harmonic mean

If n is the variety of numbers, it’s discovered by dividing the variety of numbers by the reciprocal of every quantity.

What’s the components to search out the harmonic imply of two or three numbers?

Suppose there are two numbers x1 and x2.

Suppose there are 3 numbers x1, x2, and x3.

H =

3
/
1/x1 + 1/x2 + 1/x3

Examples displaying how one can calculate the harmonic imply

Instance #1:

Discover the harmonic imply of three and 4


Instance #2:

Discover the harmonic imply of 1, 2, 4, and 10

H =

4
/
1/1 + 1/2 + 1/4 + 1/10

H =

4
/
20/20 + 10/20 + 5/20 + 2/20

A linear movement downside that results in the harmonic components.

A automobile travels with a velocity of 40 miles per hour for the primary half of the best way. Then, the automobile travels with a velocity of 60 miles per hour for the second half of the best way. What’s the common velocity? 

Common velocity =

complete distance
/
complete time

First discover that it’s not attainable to make use of straight the velocity components since we have no idea for a way lengthy the automobile saved driving with a velocity of 40 m/h after which 60 m/h. Nevertheless, with some manipulation, we are able to nonetheless deal with the issue.

Let t1 be the time it took to journey the primary half of the overall distance

Let d be the primary half of the overall distance.

Let t2 be the time it took to journey the second half of the overall distance

Let d be the second half of the overall distance.

Complete time = t1 + t2 = d/40 + d/60

Complete distance = d + d = 2nd

Now exchange these within the components

Common velocity =

complete distance
/
complete time

Common velocity =

2nd
/
d/40 + d/60

Common velocity =

2nd
/
d(1/40 + 1/60)

Cancel d and the common velocity =

2
/
(1/40 + 1/60)

Now, you possibly can see that it seems like we’re calculating the harmonic imply for two numbers through the use of the components above.

H = common velocity =

2
/
(3/120 + 2/120)

H = common velocity =

2
/
(5/120)

H = common velocity =

2 × 120
/
5

H = common velocity =

240
/
5

= 48 miles per hour

One other technique to specific the harmonic imply of n numbers

That is going to problem you a bit. Nevertheless, don’t hand over. Maintain studying and you’re going to get it! Moreover, ensure you completely perceive fractions earlier than studying this part of the lesson.

Right here is our technique:

Step 1. Specific the harmonic imply of two or three numbers otherwise.

Step 2. Study fastidiously step 1 by in search of patterns and make a generalization utilizing the summation symbols and the product symbols.

Rewriting the harmonic imply of two numbers

$$ H = frac{2}{ frac{1}{x_1} + frac{1}{x_2} } $$

$$ H = frac{2}{ frac{x_2 + x_1}{x_1 occasions x_2} } $$

$$ H = frac{2 occasions x_1x_2 }{ x_2 + x_1 } $$

$$ H = frac{2 occasions x_1x_2 }{ frac{x_1x_2}{x_1} + frac{x_1x_2}{x_2} } $$

At this level, discover that we rewrote the denominator x2 + x1. Why did we try this? We did this as a result of we would like the x1x2 to seem in three completely different locations (as soon as on high and twice on the backside)

This can assist us to issue the underside a part of the complicated fraction as you possibly can see beneath.

$$ H = frac{2 occasions x_1x_2 }{ x_1x_2(frac{1}{x_1} + frac{1}{x_2}) } $$

Rewriting the harmonic imply of three numbers

$$ H = frac{3}{ frac{1}{x_1} + frac{1}{x_2} + frac{1}{x_3} } $$

$$ H = frac{3}{ frac{x_2x_3 + x_1x_3 + x_1x_2}{x_1 occasions x_2 occasions x_3} } $$

$$ H = frac{3 occasions x_1x_2x_3 }{ x_2x_3 + x_1x_3 + x_1x_2 } $$

$$ H = frac{3 occasions x_1x_2x_3 }{ frac{x_1x_2x_3}{x_1} + frac{x_1x_2x_3}{x_2} + frac{x_1x_2x_3}{x_3} } $$

Discover once more that we rewrote the denominator x2x3 + x1x3 + x1x2. Why did we try this? We did this as a result of we would like the x1x2x3 to seem in 4 completely different locations (as soon as on high and 3 times on the backside)

Once more, this can assist us to issue the underside a part of the complicated fraction as you possibly can see beneath.

$$ H = frac{3 occasions x_1x_2x_3 }{ x_1x_2x_3(frac{1}{x_1} + frac{1}{x_2} + frac{1}{x_3}) } $$

Abstract

For two or 3 numbers, here’s what we’ve up to now!

$$ H = frac{2 occasions x_1x_2 }{ x_1x_2(frac{1}{x_1} + frac{1}{x_2}) } $$

$$ H = frac{3 occasions x_1x_2x_3 }{ x_1x_2x_3(frac{1}{x_1} + frac{1}{x_2} + frac{1}{x_3}) } $$

For n numbers, here’s what we could have then!

$$ H = frac{n occasions x_1x_2x_3 … x_n }{ x_1x_2x_3 … x_n(frac{1}{x_1} + frac{1}{x_2} + frac{1}{x_3} +… + frac{1}{x_n}) } $$

For n numbers, we are able to make the components look slightly higher or extra generalized through the use of the summation image and the product image talked about earlier. Utilizing the product image, we get:

$$ H = frac{n occasions prod_{j=1}^n x_j }{ prod_{j=1}^n x_j(frac{1}{x_1} + frac{1}{x_2} + frac{1}{x_3} +… + frac{1}{x_n}) } $$

And utilizing additionally the summation image, we get:

$$ H = frac{n occasions prod_{j=1}^n x_j }{ prod_{j=1}^n x_j(sum_{i=1}^n frac{1}{x_i}) } $$

$$ H = frac{n occasions prod_{j=1}^n x_j }{ (sum_{i=1}^n frac{prod_{j=1}^n x_j}{x_i}) } $$


See an instance of harmonic imply associated to the inventory market. 


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