straight lines

r267747

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Oct 1, 2009
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A line forms a triangle with coordinate axes. If the area of this triangle is 54sq.root3 squ. units & the perpendicular drawn from the origin to the line makes an angle of 60 with the x-axes. find the =n of the line.
Sir, here I don't know how to find the =n of the line using area.
 
You have 2 possible line equations, for triangles sitting on top of the x-axis.
i'm assuming =n is short for equation.

Suppose the triangle sits on the positive half of the x-axis from zero to infinity.

If the perp from the origin to the line is 60 degrees.
then the line makes an angle of 30 degrees with the x-axis.

Be sure this is clear before proceeding,
draw a diagram if necessary.

\(\displaystyle tan30^o=\frac{1}{\sqrt{3}}\)

this gives us the ratio of height over base.

Therefore height=k and base=\(\displaystyle k\sqrt{3}\)

Be sure that you are clear about this before proceeding......\(\displaystyle \frac{k}{k\sqrt{3}}=\frac{1}{\sqrt{3}}\)

Now use the area to discover k.

Triangle area is \(\displaystyle 0.5(k)k\sqrt{3}=54\sqrt{3}\)

\(\displaystyle k^2=108\)

\(\displaystyle k=\sqrt{108}\)

The line slope \(\displaystyle m=-\frac{1}{\sqrt{3}}\)

\(\displaystyle c=k=\sqrt{108}\)

The equation is y=mx+c.

What about working out the 2nd one?
 
There are actually 4 lines - one in each quadrant.
 
One makes an angle of 60 degrees,
the next makes an angle of 120 degrees,
the next makes an angle of 240 degrees
and the last one makes an angle of 300 degrees...

maybe we should just concentrate on one.
 
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