d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}
M = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right)
m = \frac{y_2 - y_1}{x_2 - x_1}
y = mx + b
m: slope
b: y-intercept
y - y_1 = m(x - x_1)
A = \frac{1}{2}ab \sin(C)
a, b: two sides
C: included angle
A = \frac{\theta}{360^\circ} \cdot \pi r^2
\theta: central angle in degrees
r: radius
x = x_1 + k(x_2 - x_1)
y = y_1 + k(y_2 - y_1)
k = \frac{m}{m + n}, where m:n is the ratio
\text{Density} = \frac{\text{Mass}}{\text{Volume}}
(x - h)^2 + (y - k)^2 = r^2
Center: (h, k)
Radius: r