alright...so i don't know everything.

1/a + 1/b= 1/c for a

i get:

1/a = 1/c - 1/b
1/a = b-c/cb

ok this is what i don't understand...

the solution is:

a = cb/b-c

i guess i understand that you invert the 1/a to make it a/1 which ='s "a"
but why wouldn't you change the sign of b-c/cb
to make it -cb/-b+c?

if i don't figger this out i'll never get that job at N.A.S.A

thanks

danny...PH.d candidate M.I.T

You could, but that would be equal to -a, not a, because you'd have to multiply both sides by -1.

The reason is that multiplying by the inverse doesn't change the sign, it just eliminates the fraction.

The inverse of one side of the equation ='s the inverse of the other side. That is because if you raise both sides of the equation to the same power, you don't change the equation. In this case, you are raising each side to the (-1) power; is that where you got the idea of changing the sign of the other part? As MX2 said, taking the inverse of a number does not change its sign. It just reverses the fraction.