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## Main Question or Discussion Point

This is a problem from a Calc 1 text book, I just can't figure out where they get dx from. The question is:

Use differentials to approximate the value of the expresesion.

[tex]\sqrt{99.4}[/tex]

the answer in the solution manual says:

Let [tex]f(x)=\sqrt{x}, x=100, dx=-.6[/tex]

then it solves the problem. But what I don't understand is where the heck is this dx quantity derived from?

Use differentials to approximate the value of the expresesion.

[tex]\sqrt{99.4}[/tex]

the answer in the solution manual says:

Let [tex]f(x)=\sqrt{x}, x=100, dx=-.6[/tex]

then it solves the problem. But what I don't understand is where the heck is this dx quantity derived from?