Find the area of a circle circumscribing an equilateral triangle of side 15cm.
take pi = 3.14.

236 cm²

Step-by-step explanation:

Height of an equilateral triangle (h) = √3 /2 (l)

l = side of the equilateral triangle.

h = √3 /2 (15)

In an equilateral triangle the orthocenter, centroid, circumcenter and incenter are in the same spot

The center of the circle is the centroid and height match  with the median. The radius of the circumcircle is equal to two thirds the height.

Formula for the Radius of the circumcircle = 2/3 h

= 2/3 x √3 /2 (15)

= 5 √3 cm     (=radius)

Area of the circle = πr^

= 3.14 x( 5 √3 ) ^

=3.14 x(25*3)

=3.14 x 75

=235.5

=236 cm²

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.

step-by-step explanation: