# A simple math equation solving for unknown

1. Dec 19, 2012

### eXmag

1. The problem statement, all variables and given/known data

Solve for A
27 = 81/√3a-3

2. Relevant equations

3. The attempt at a solution

Im not sure where to begin with this question. Can someone go through all the steps into solving for A. Thanks

2. Dec 19, 2012

### JimRoo

Is it sqrt(3a - 3) or sqrt(3a) - 3 or sqrt(3) * a - 3.

Whatever value of "a" is in the denominator, it has to be moved to the numerator, usually by multiplying both sides of the equation by the appropriate term containing "a". If it's sqrt(3a - 3) then multiply both sides of the equation by sqrt (3a - 3) to get:

27 * sqrt(3a - 3) = 81.

Then continue to solve for "a".

3. Dec 19, 2012

### tensor33

Multiply both sides by sqrt(3a-3). It should be pretty straightforward from there
Edit:never mind someone else answered it first

4. Dec 19, 2012

### SammyS

Staff Emeritus
Begin by using enough sets of parentheses to make the problem unambiguous.

Is it

$\displaystyle 27=\frac{81}{\sqrt{3a-3\,}}$

or

$\displaystyle 27=\frac{81}{\sqrt{3a\,}-3}$

or

$\displaystyle 27=\frac{81}{\sqrt{3\,}\,a-3}$

or

$\displaystyle 27=\frac{81}{\sqrt{3a\,}}-3$

or what it means literally with there being no parentheses

$\displaystyle 27=\frac{81}{\sqrt{3\,}}a-3$

?

5. Dec 19, 2012

### eXmag

yes I should have mentioned it is square root 3a-3 not square root 3a then minus 3. Ok thanks for the responses.

6. Dec 19, 2012

### eXmag

^the first example you gave sammy, how would I go through the steps to solve for A?

7. Dec 19, 2012

### SammyS

Staff Emeritus

Square both sides.

8. Dec 19, 2012

### eXmag

Ok, sorry Im not really math literate. How would you isolate the radical?

9. Dec 19, 2012

### eXmag

ok so im gonna go through it.

27 x √3a-3 = 81
√3a-3 = 81/27
√3a-3 = 3
3a-3 = 9
3a = 9 + 3
3a = 12
a = 12/3
a = 4

10. Dec 19, 2012

### SammyS

Staff Emeritus
Now, check your answer by plugging into the original problem.

11. Dec 19, 2012

### eXmag

perfect...thank you very much sammy!