Re: Need a quick response Please

On Thu, 19 Feb 2009 19:11:05 -0800 (PST), Fem_beginner_level
<aligatoral@xxxxxxxxx> wrote:

On Feb 19, 9:52 pm, quasi <qu...@xxxxxxxx> wrote:
On Thu, 19 Feb 2009 18:27:21 -0800 (PST), Fem_beginner_level



<aligato...@xxxxxxxxx> wrote:
On Feb 19, 9:15 pm, Fem_beginner_level <aligato...@xxxxxxxxx> wrote:
On Feb 19, 9:08 pm, Robert Israel

<isr...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Fem_beginner_level <aligato...@xxxxxxxxx> writes:
Find the smallest positive angle, to the nearest degree, between the
lines l1 and l2.

l1: y =(2/3)x + 6
l1: y =2x - 5

could you tell me how to solve the question , i couldnt understand
what does it mean.

Two intersecting straight lines have two different angles between them.
You're asked for the smaller of the two, the one that's more than 0 and less
than 90 degrees.  
--
Robert Israel              isr...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Department of Mathematics        http://www.math.ubc.ca/~israel
University of British Columbia            Vancouver, BC, Canada

thanks robert

l1: y=(2/3)x+6

A(0,6) B(-9,0)

l2:

C(0,-5) D(5/2,0)

i still couldnt get the angle...

Quasi,

COB is a straight line not a triangle ???

For the point O, use the point of intersection of the 2 lines.

From the point O, go 1 unit to the right and call that point A.

For B, go vertically up from A, a distance of 2/3.

For C, go vertically up from A, a distance of 2.

The points B and C are on your respective lines. Can you see how we
forced that by the choice of distances up from A?

Note that triangles OAB and OAC are right triangles (one is inside the
other).

You should be able to get all the side lengths.

Now look at triangle COB.

Isn't angle COB the angle you want?

Ok, so then follow my prior hints (law of cosines, etc).

quasi

actually i tried my own points and found the answer thanks for your
help.

Cos(teta)=0.8682

That's the right answer for cos(theta).

Don't forget to do arccos to get the angle.

thank you

No prob.

quasi
.

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