# ARC of the function - write an equation that represents the statement

I'm missing something on this problem: "As you go deeper into a cave, the light intensity gradually decreases until it becomes very dark. Let L(d) denote the light intensity in a certain cave L (measured in cd/sq. m) at a given depth d (measured in m). Write an equation that represents the following statement:

The light intensity 4m inside the cave is 3000 cd/sq. m less than the light intensity at the entrance to the cave. "

I wrote L(4)-L(0)/4=-3000

But it turned out to be wrong and I don't know what it is. What did I do wrong?

The light intensity at the entrance is $L(0)$.

The light intensity $4$m deep is $L(4)$

What the sentence is basically saying is "this one number is this much bigger than that other number". And the sentence "$x$ is $c$ bigger than $y$" can easily translate into math as

$$x=y+c$$

or $$x-y=c.$$

You do the rest.

• $L(0)=L(4)+3000$ ? – Steve May 12 '17 at 8:23
• @Steve It's as simple as that, yeah – 5xum May 12 '17 at 8:25
• – Steve May 12 '17 at 8:37