Hi, my algebra is quite rusty and I can't figure this one out.

$\displaystyle c_3 = \frac{y_3-y_1}{(x_3-x_1)(x_3-x_2)} - \frac{y_2-y_2}{(x_3-x_2)(x_2-x_1)}

$

My book says that "by taking a common denominator we get",

$\displaystyle c_3 = \frac{\frac{y_3-y_2}{x_3-x_2}-\frac{y_2-y_2}{x_2-x_2}}{x_3-x_1} $

If I was to find a common denominator for this, it would look something like this,

$\displaystyle c_3 = c_3 = \frac{y_3-y_1(x_2-x_1)}{(x_3-x_1)(x_3-x_2)(x_2-x_1} - \frac{y_2-y_2(x_3-x_1)}{(x_3-x_2)(x_2-x_1)(x_3-x_1)}$

I've played with it for a while, but can't seem to arrive at the right expression..

Any tips besides finding another hobby?