Find the area of a circle with the circumference 18(pi)

D 81 pi units^2

Step-by-step explanation:

The circumference of a circle  is given by

C = 2 * pi *r

18 pi = 2 * pi *r

Divide each side by 2 * pi

18 pi / (2 pi) = 2 pi * r/ (2 pi)

9 = r

Now we can find the area.  Area is given by

A = pi r^2

A = pi * 9^2

A = 81 pi units^2

Circumference =

18 ÷ 2 = 9

r = 9

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Area =

=

= 81 units².

for the points! : )

3. parallelogram

step-by-step explanation:

we turn each of our sides into direction vectors

ab=b-a=(3 - 7, 1 - 0) = (-4, 1)

bc=c-b=(1,6)

cd=d-c=(4,-1)

da=a-d=(-1,-6)

we see how the opposite sides have negated direction vectors; this is characteristic of a parallelogram.   we have congruent sides ab=cd and bc=da with unequal lengths because 1^2+6^2 is different from (-4)^2+1^2.   so it's not a square or a rhombus.  

we check the dot product of direction vectors of adjacent sides.   we have

ab dot bc = -4(1) + 1(6) = 2

that's not zero so the sides are not perpendicular.   we've ruled out rectangle.

the direction vectors indicate two pairs of congruent parallel sides, so we choose parallelogram over trapezoid.