We consider the circles (C) (O; 9) and (C ’) (O’; 4) tangent on the outside. To calculate the area of the surface between the two circles and a tangent
common to both circles: show that this surface is obtained by the difference between
that of a rectangular trapezoid and those of two disk sectors.
So calculate the area.

2 1/2 feet

step-by-step explanation:

the answer is a and d

x^2 + 81

we can factor this using difference of square binomials.

rewrite the equation:

x^2 - (-81)

factor:

(a^2 - b^2) = (√a^2 + √b^2)(√a^2 - √b^2)

(x^2 - (-81) = (x + √-81)(x - √-81)

we can remove the - from under the radical by multiplying it by i.

(x^2 - (-81) = (x + i√81)(x - i√81)

(x^2 - (-81) = (x + 9i)(x - 9i)

we can check our answer by using foil:

x^2 - 9ix + 9ix - 81i^2

x^2 - 81^2

i^2 = -1

x^2 + 81