The formula for the area of a circle can be found by using a parallelogram. Explain the way to derive the formula.

If the other answer doesn't work, try this:

The circle can be cut into slices, separated, and fit together to form a parallelogram that has the same area. The height of the parallelogram is the radius and the base is half the circumference, which is r. The area is r(r), which is equal to r2.

Step-by-step explanation:

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