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Semenov [28]
3 years ago
15

When an electric current passes through two resistors with resistance r1 and r2, connected in parallel, the combined resistance,

R, can be calculated from the equation 1R=1r1+1r2, where R, r1, and r2 are positive. Assume that r2 is constant.
(a) Show that R is an increasing function of r1.

(b) Where on the interval a≤r1≤b does R take its maximum value?
Mathematics
1 answer:
kondaur [170]3 years ago
6 0

Answer:

a)

The combined resistance of a circuit consisting of two resistors in parallel is given by:

\frac{1}{R}=\frac{1}{r_1}+\frac{1}{r_2}

where

R is the combined resistance

r_1, r_2 are the two resistors

We can re-write the expression as follows:

\frac{1}{R}=\frac{r_1+r_2}{r_1r_2}

Or

R=\frac{r_1 r_2}{r_1+r_2}

In order to see if the function is increasing in r1, we calculate the derivative with respect to r1: if the derivative if > 0, then the function is increasing.

The derivative of R with respect to r1 is:

\frac{dR}{dr_1}=\frac{r_2(r_1+r_2)-1(r_1r_2)}{(r_1+r_2)^2}=\frac{r_2^2}{(r_1+r_2)^2}

We notice that the derivative is a fraction of two squared terms: therefore, both factors are positive, so the derivative is always positive, and this means that R is an increasing function of r1.

b)

To solve this part, we use again the expression for R written in part a:

R=\frac{r_1 r_2}{r_1+r_2}

We start by noticing that there is a limit on the allowed values for r1: in fact, r1 must be strictly positive,

r_1>0

So the interval of allowed values for r1 is

0

From part a), we also said that the function is increasing versus r1 over the whole domain. This means that if we consider a certain interval

a ≤ r1 ≤ b

The maximum of the function (R) will occur at the maximum value of r1 in this interval: so, at

r_1=b

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3 years ago
Question 1: Explain how the letter x (or any letter) is used when writing expressions, and give an example. How are expressions
BaLLatris [955]

Answer:

Question 1:

The letter x or any letter used when writing an expression is representative of  unit of an idea, quantity or measure, such that it can be translated in the expression to provide information about a related idea

Question 2:

The expression can be translated as two times the expression three (variable) x minus two (variable) y plus the constant 7

Question 3:

In the first expression, the like terms are;

10y and (-2y),

3x and x

In the second expression, the like terms are;

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The first expression simplifies to 8y + 4x + 10

The second expression simplifies to  7x - 3y + 6

Question 4:

The expression is evaluated as 122

Question 5:

The equivalent expression of the expression 3(4x + 2y) + 5x, is 17x + 6y

To prove when x = 1 and y = 2 we have;

3(4×1 + 2×2) + 5×1 is 29

17×1 + 6×2 is 29 which are equivalent in value

Step-by-step explanation:

Question 1:

The letter x or any letter used when writing an expression is representative of  unit of an idea, quantity or measure, such that it can be translated in the expression to provide information about a related idea

Example;

If x is the symbol representing the average number of oranges sold in 1 hour, then the expression for the number of oranges sold per day of 24 hours  = 24·x

An expression is a written mathematical symbolic statement that shows the the finite merging together of representative symbols by the mathematical operations that govern the present constraints

An equation is a statement that two expressions are equal

Question 2:

The given expression is 2(3x - 2y) + 7

The parts are;

The coefficient of (3x - 2y) = 2

The constant term = 7

The variables are x and y

Which gives

The coefficient of the variable x = 6

The coefficient of the variable y = -4

The expression can be translated as two times the expression three (variable) x minus two (variable) y plus the constant 7

or

The expression can be translated as two times the bracket open three times (variable) x minus two times (variable) y bracket close plus the constant 7

or

The expression can be expanded as 2(3x - 2y) + 7 → 6·x - 4·y + 7 which is expressed verbally as follows;

Six times (variable) x minus four times (variable) y plus the constant 7

Question 3:

The expressions are;

10y + 3x + 10 + x  - 2y..........................(1)

3x - y + 4x + 6 - 2y,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,(2)

In the first expression, the like terms are;

10y and (-2y),

3x and x

In the second expression, the like terms are;

-y and -2y

3x and 4x

They are like terms because they can be simply added together to simplify the expressions as follows

10y + 3x + 10 + x  - 2y gives 10y - 2y + 3x + x  10  to give 8y + 4x + 10

Also

3x - y + 4x + 6 - 2y  gives  3x+ 4x - y  - 2y + 6 to give 7x - 3y + 6

Question 4:

The expression 8x² + 25·y when x = 3 and y = 2 is evaluated by replacing (putting) the value x and y (into the expression)

The expression is then evaluated as 8×3² + 25×2 which is the same as 72 + 50 or 122

Question 5:

To write the equivalent expression of the expression 3(4x + 2y) + 5x, we expand the expression as follows;

3×4x + 3×2y + 4x which is 12x + 6y + 4x

We combine like terms;

12x + 5x + 6y which is 17x + 6y

To prove we can check by substituting a value for each of the variables x and y such as x = 1 and y = 2

3(4×1 + 2×2) + 5×1 is 29

17×1 + 6×2 is 29

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skelet666 [1.2K]

Answer:

The answer to the question is

1.5 hours that is;

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Step-by-step explanation:

We note that

The speed of the military convoy headed north =50 mph

The speed of the convoy headed south  = 40 mph

Let t be the time taken for the two convoys to be 135 miles apart

The time taken for the two convoys to be 135 miles apart is given by

50×t miles+ 40×t miles= 135 miles

That is 90×t miles = 135 miles

                  t = 135/90 = 1.5 hrs

3 0
3 years ago
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