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.

3a - 7a = -4a

The formula for circumference is circle diameter x π:

c = πd
c = 7π

To solve this equation, repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

-4a - 4 = \( \frac{a}{-5} \)
-5 x (-4a - 4) = a
(-5 x -4a) + (-5 x -4) = a
20a + 20 = a
20a + 20 - a = 0
20a - a = -20
19a = -20
a = \( \frac{-20}{19} \)
a = -1\(\frac{1}{19}\)

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.

An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite:

d° = b° + c°

To find angle c, remember that the sum of the interior angles of a triangle is 180°:

180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 69° - 37° = 74°

So, d° = 37° + 74° = 111°

A shortcut to get this answer is to remember that angles around a line add up to 180°:

a° + d° = 180°
d° = 180° - a°
d° = 180° - 69° = 111°