The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

8a - 4a = 4a

The entire length of this line is represented by AD which is AB + BD:

AD = AB + BD

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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

2c + x = 8
x = 8 - 2c

then substitute the result (8 - 2c) into the second equation:

-2c + 1(8 - 2c) = -2
-2c + (1 x 8) + (1 x -2c) = -2
-2c + 8 - 2c = -2
-2c - 2c = -2 - 8
-4c = -10
c = \( \frac{-10}{-4} \)
c = 2\(\frac{1}{2}\)