[SOLVED] Mathmatical concept(square root of min*max)

[petelee]

When I studied electronic circuit design book, I encountered this mathematical thing.

If X has this range (a < X < b), then the suggested X value is like this.

X = SQRT(a*b).

It's not average or something else. I don't remember this thing from my old math study. Could you anybody help me with the mathematical concept name so that I can refer to website?

Thanks in advance!!

 

[lazyzyf]

x=sqrt(a^2+b^2)
is that right?

 

[godfreyl]

X = SQRT(a*b).

That's the geometric mean.

x=sqrt(a^2+b^2)

That's the RMS value.

 

[Tunelabguy]

X = SQRT(a*b).

As godfreyl said, it is the geometric mean. Its value in setting X between the min and max (a and b) is this: Suppose that the value you set for X is only an initial value and that it might change over time. And suppose you want to be assured that even after X changes it will still remain between a and b. And suppose that the amount X changes is proportional to the initial value of X. Then the best you can do to assure X stays between a and b is to use the geometric mean.

 

[petelee]

Thanks a lot! Now I know what it is.