Angle between 2 straight lines - Notes (1 Viewer)

nrlwinner · Apr 25, 2009

Hi. I have copied some notes in class and didn't get to finish them. If you can sort of help me complete the point, it would benefit my studies.

Note:

1)If m1m2 = -1, the lines are perpendicular
ie theta = 90degrees
tan theta is undefined

2)If m1=m2, the lines are parallel
ie theta = 0degrees
tan theta = 0

3)Between any pair of intersecting lines there is one acute and one obtuse angle. (haven't finished this point)

oly1991 · Apr 25, 2009

You would solve the equations simultaneously to see where they intersect.

To find the acute angle you would use the formula:

tan@ = m1-m2/1+m1m2

You can then subtract this from 180 to find the obtuse angle.

Hope that helps a bit.....

Drongoski · Apr 25, 2009

If the 2 lines L1 and L2 have gradients m1 and m2 then

m1 = tan (theta1) and m2 = tan (theta2)

$Then\ \ \ tan(\theta _{2}-\theta _{1})\ =\ \frac{m_{2}\ -\ m_{1}}{1\ +\ m_{1}m_{2}}\ \ \ \ \ (provided \ m_{1}m_{2}\ \neq -1)\\ \\ The\ angle\ between\ L_{1}\ and\ L_{2}\ \ is\ tan^{-1}\left (\frac{m_{2}\ -\ m_{1}}{1\ +\ m_{1}m_{2}} \right )\\ \\ The \ angle\ between\ the\ 2\ lines\ \ is\ acute\ if \ the \ fractional\ expression\ is\ positive\\ \\ \ and\ obtuse\ if\ it\ is\ negative.$

But I'm sure you will find all these in your textbooks; read them. Shouldn't mean you are completely helpless without your teacher's notes.

Angle between 2 straight lines - Notes (1 Viewer)

nrlwinner

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oly1991

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Drongoski

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