What is the exact area of a circle whose diameter is 18 cm? a. 9 straight pi cm2 b. 18 straight pi cm2 c. 36 straight pi cm2 d. 81 straight pi cm2

The formula for the area of a circle is:

A=πr²

We also know that the diameter of a circle is twice the size of its radius

d=2r

So if the diameter is 18...

18=2r

divide both sides by 2

9=r

The radius of the circle is equal to 9cm

Now we can solve for the area

A=πr²

A=π9²

A=π81

A=81πcm²

The exact area of a circle whose diameter is 18cm is 81πcm²

Answer=D

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)