Monday

December 22, 2014

December 22, 2014

Posted by **Kristal** on Sunday, November 12, 2006 at 7:25pm.

This is the question:

Find an equation of the line through the point (1,3) that cuts off the least area from the first quadrant.

My work on the problem so far:

I know that it will be in the first quadrant and that the result will form a right triangle.

I have written the equation y=-mx+b because I do know that the line will be decreasing.

Besides that, I do not know what to do.

Can someone help me please?

If you take the equation for the line to be:

y=-mx+b (1)

then you have to require that if x = 1, y = 3. So, you insert these figures in Eq. (1) and you get:

3 = -m + b (2)

This equation does not fix m and b but relates the two. This is what you would expect, because you can draw a line through the point (1,3) in an infinite number of ways. You then calculate where the line will intersect the x-axis. At that point y=0, so:

-mx + b =0 -->

x = b/m

And the line intersects the Y-axis when x = 0, so the y-coordinate at that point is b.

This maens that the right traingle as its three corners at:

(0,0), (0,b) and (b/m,0)

The area of the triangle is thus:

A = 1/2 b^2/m (3)

If you use Eq. (2) to express b in terms of m:

b = 3 + m and insert that in (3), you find:

A = 1/2 (3 + m)^2/m =

1/2 (9/m + 6 + m)

If you equate the derivative of this to zero you find:

m = 3.

**Answer this Question**

**Related Questions**

SAT Math... again - I asked two questions yesterday, and thankfully, bobpursley ...

AP Calculus - I asked this yesterday and someone answered. but i didn't ...

English-A Raisin in the Sun - Also a continued post from yesterday: I am ...

AED 200 - I asked a question about reliable sources yesterday. My problem is I ...

Not exactly homework question - Alright, so I know this isn't exactly what i ...

Math Riddle - What day would yesterday be if Wednesday was five days before the ...

Science - I have to research about Francisco Redi's Spontaneous Generation. I am...

Algebra2 - i was wondering if someone could check the answer i got for this math...

Calculus - We are doing problems with the product and quotient rules, but I'm ...

math - i asked a question yesterday and i got an answer. my question was how ...