Question

Find the constant of proportionality k. Then write an equation for the relationship between x and y

Answer 1

Question:

Find the constant of proportionality k. Then write an equation for the relationship between x and y

$\begin{array}{ccccc}x & {2} & {4} & {6} & {8} \ \\ y & {10} & {20} & {30} & {40} \ \ \end{array}$

Answer:

(a) $k = 5$

(b) $y = 5x$

Step-by-step explanation:

Given

$\begin{array}{ccccc}x & {2} & {4} & {6} & {8} \ \\ y & {10} & {20} & {30} & {40} \ \ \end{array}$

Solving (a): The constant of proportionality:

Pick any two corresponding x and y values

$(x_1,y_1) = (2,10)$

$(x_2,y_2) = (6,30)$

The constant of proportionality k is:

$k = \frac{y_2 - y_1}{x_2 - x_1}$

$k = \frac{30-10}{6-2}$

$k = \frac{20}{4}$

$k = 5$

Solving (b): The equation

In (a), we have:

$(x_1,y_1) = (2,10)$

k can also be expressed as:

$k = \frac{y- y_1}{x- x_1}$

Substitute values for x1, y1 and k

$5 = \frac{y- 10}{x- 2}$

Cross multiply:

$y - 10 = 5(x - 2)$

Open bracket

$y - 10 = 5x - 10$

Add 10 to both sides

$y - 10 +10= 5x - 10+10$

$y = 5x$