Word Problems,The illumination at a point is inversely proportional to the square

I have two word problems that I do not know what to do. can some please explain how to I solve this.

Quote:

The illumination at a point is inversely proportional to the square of the distance of the point from the light source and directly proportional to the intensity of the light source. If two light sources are **s **feet apart and their intensities are ** I** and **J** respectively, at what point between them will the sum of their illuminations be a minimum? Instruction: Give your answer in terms of **s**, **I **and **J **.

Solution:

Let **x **be the distance from *I *at which the sum of the illuminations be minimum. Then

x= ______

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Quote:

Find the equation of the line that is tangent to the ellipse

http://img.photobucket.com/albums/v6...25750img13.gif in the first quadrant and forms with the coordinate axes the triangle with smallest possible area (

**a **and

**b **are positive constants.)

The equation of the required line is:

____x + ____y + ______ = 0