Combined variation: Light intensity varies inversely as....

[jshaziza]

The intensity I of light varies inversely as the square of distance d from the light source. If the distance from the light source is double, determine what happens to the intensity of light at the new location. Assume the initial distance form a lamp to a book is 12 inches, and the new distance is 24 inches.

I wasn't able to figure out how to translate this problem into a formula. If someone could translate this problem into a formula for me, I can take it from there. thx for your help.

 

[jshaziza]

Question

Does the graph of every quadratic function have a y-intercept? Why or why not?

For this question I at first thought no, not every function has a y-intercept, because if the vertex is off the x axis or y axis lines, the parabola doesn't necessearily need to cross the y-intercept line. But I got confused because I am not sure if they count the fact that the lines of the parabola in almost any case if it is extended will cross the y-intercept. Could you guys clear this up for me? thx.

 

[skeeter]

Re: Combined variation

The intensity I of light varies inversely as the square of distance d from the light source. If the distance from the light source is double, determine what happens to the intensity of light at the new location. Assume the initial distance form a lamp to a book is 12 inches, and the new distance is 24 inches.

I = k/d² ... double "d" and what happens to I ???

Does the graph of every quadratic function have a y-intercept? Why or why not?

no ... look at the graph of y = x² + 1

 

[tkhunny]

Just don't try it at d = 0.

 

[Deleted member 4993]

Every quadratic function of the form

y = Ax^2 + Bx + C

does have a y-intercept (which is the value of y at x =0)

So if the quadratic function is y = f(x) then it will have a y-intercept.

It may not have a x-intercept. When it does have x-intercept, it will have a pair of those.

 

[skeeter]

SK is correct ... I read y-intercept and thought x-intercept.