F is inversely proportional to d^2. When F = 14, d = 5 Work out d
(positive value rounded to 2 DP) when F = 3

d ≈ 10.80

Step-by-step explanation:

Given F is inversely proportional to d² then the equation relating them is

F = ← k is the constant of variation

To find k use the condition F = 14, d = 5 , then

14 = = ( multiply both sides by 25 )

350 = k

F = ← equation of variation

when F = 3 , then

3 = ( multiply both sides by d² )

3d² = 350 ( divide both sides by 3 )

d² = ( take square root of both sides )

d = ≈ 10.80 ( positive value to 2 dec. places )

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional