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° - 66° = 45°

So, d° = 66° + 45° = 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°

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

x² + 4x - 12 = 0
(x - 2)(x + 6) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 2) or (x + 6) must equal zero:

If (x - 2) = 0, x must equal 2
If (x + 6) = 0, x must equal -6

So the solution is that x = 2 or -6

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.

8a⁹ + 3a⁹ = 11a⁹

The slope-intercept equation for a line is y = mx + b where m is the slope and b is the y-intercept of the line. From the graph, you can see that the y-intercept (the y-value from the point where the line crosses the y-axis) is -2. The slope of this line is the change in y divided by the change in x. The endpoints of this line segment are at (-2, -4) and (2, 0) so the slope becomes:

Plugging these values into the slope-intercept equation:

y = x - 2

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.

2a⁷ - 2a⁷ = 0a⁷