Maths: Help me!

October 24, 2007 6:26 PM

Time for a ridiculous math question: I've got F=255M^(-1.08) and I need to work out M.

It is driving me crazy that I can't work this out.

[[not a homework question]]

Thanks in advance!

posted by cholly to science & nature (10 comments total)

Do you have F? Or do you need to express M as a function of F?
posted by neustile at 6:29 PM on October 24, 2007

M = (255/F)^(1/1.08)
posted by number9dream at 6:31 PM on October 24, 2007

Divide both sides by 255: F/255 = M^(-1.08)

Ln both sides and drop down the exponent: ln(F/255) = -1.08ln(M)

Divide both sides by -1.08: ln(F/255)/-1.08

Raise e to the power of each side.

M = e^(ln(F/255)/-1.08)
posted by dondiego87 at 6:31 PM on October 24, 2007

dondiego, taking ln of both sides and then e^both sides is redundant.
posted by number9dream at 6:32 PM on October 24, 2007

The third line ends "= ln(M)"
posted by dondiego87 at 6:32 PM on October 24, 2007

But... didn't it work?
posted by dondiego87 at 6:32 PM on October 24, 2007

M = (F/255)^(1/-1.08)
posted by jpdoane at 6:33 PM on October 24, 2007

number9dream - beat me to it

dondiego- you're not solving for the exponant, so you don't need a log. It worked, but you did several pointless steps
posted by jpdoane at 6:35 PM on October 24, 2007

Thanks guys! My maths is a little rsuty. =]
posted by cholly at 6:36 PM on October 24, 2007

But it's so much more fun that way! ;-)

Okay, I admit it, I haven't taken any math in 2 years.
posted by dondiego87 at 7:13 PM on October 24, 2007