Thread: Solve for the specified variable?

1. Solve for the specified variable?

What do I do, I'm the HORRIBLE when it comes to math :'( I have a lot more of these but i need to learn how to do this.

1/a + 1/b = c for a

P= A/1+rt for r

I= kE/R for R

2. $\displaystyle \frac{1}{a}+\frac{1}{b}=c$

Start by removing the fractions (just multiply through by the denominators, as below):

$\displaystyle a(\frac{1}{a}+\frac{1}{b})=a\times c$

$\displaystyle 1+\frac{a}{b}=ac$

$\displaystyle b(1+\frac{a}{b})=ac\times b$

$\displaystyle b+a=abc$

Rearrange so that all terms involving 'a' are on one side of the equation:

$\displaystyle b=abc-a$

Factor out an $\displaystyle a$:

$\displaystyle b=a(bc-1)$

Divide through by the non-a factor:

$\displaystyle \frac{b}{bc-1}=a$

Try the others yourself, it's the same principle! Post your working if you're still unable to continue.

3. Originally Posted by mrmyers22
1/a + 1/b = c for a
Multiply each term by ab:
b + a = abc
Get the terms with "a" together:
abc - a = b
factor left side:
a(bc - 1) = b
divide each side by (bc - 1):
a = b / (bc - 1)