Writing the equation of the line...

• Feb 22nd 2010, 09:56 AM
PiratePrincess
Writing the equation of the line...
Hi there can you help me find the equation of the line that has a slope of -4/3 and passes through (-2,5) ?

Thank you!
• Feb 22nd 2010, 10:12 AM
mathemagister
Quote:

Originally Posted by PiratePrincess
Hi there can you help me find the equation of the line that has a slope of -4/3 and passes through (-2,5) ?

Thank you!

The formula for the equation of a line knowing 2 points and a slope is:

$\displaystyle y-y_1 = m(x-x_1)$ where m is the slope and $\displaystyle x1$ and $\displaystyle y1$ are the coordinates of the given point.

Simply substitute:

$\displaystyle y-5 = -\frac{4}{3} (x- (-2))$ and clean up if you want. Usually, on AP Calc tests, they recommend you don't waste your time simplifying because they accept this answer.
• Feb 22nd 2010, 03:04 PM
integral
$\displaystyle y=ax+b$
$\displaystyle a=m=\frac{-4}{3}$

$\displaystyle 5=\frac{-4}{3}(-2)+b$
$\displaystyle 5=\frac{8}{3}+b$
$\displaystyle b=5-\frac{8}{3}$
$\displaystyle b=\frac{7}{3}$

$\displaystyle y=\frac{-4}{3}x+\frac{7}{3}$

Just as a different method (Bow)