A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

The formula for area is πr²:

a = πr²
a = π(5²)
a = 25π

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(8a)(9ab) + (5a²)(7b)
(8 x 9)(a x a x b) + (5 x 7)(a² x b)
(72)(a¹⁺¹ x b) + (35)(a²b)
72a²b + 35a²b
107a²b

You need to find the value of c so solve the first equation in terms of y:

-9c + y = -1
y = -1 + 9c

then substitute the result (-1 - -9c) into the second equation:

-4c - 4(-1 + 9c) = 2
-4c + (-4 x -1) + (-4 x 9c) = 2
-4c + 4 - 36c = 2
-4c - 36c = 2 - 4
-40c = -2
c = \( \frac{-2}{-40} \)
c = \(\frac{1}{20}\)

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(9a)(9ab) - (4a²)(8b)
(9 x 9)(a x a x b) - (4 x 8)(a² x b)
(81)(a¹⁺¹ x b) - (32)(a²b)
81a²b - 32a²b
49a²b