15 : find the equation of the tangent line to the parabola y=x^2 at the point (2, 4). hint: a line y-4=m(x-2) is the tangent to the parabola if and only if the line is non-vertical and the nonlinear system
y=x^2
y=m(x-2)+4
has exactly one solution.

Yeap, thus

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.