# Homework Help: Subject element from formula

1. May 24, 2013

### PA3040

1. The problem statement, all variables and given/known data
Subject the "PR2" from the following equation

2. Relevant equations
Tpwm = [(PR2) + 1] • 4 • TOSC • N

• = multiply

3. The attempt at a solution

Actually I am not a student
As well as I know how the equation after subject the "PR2"... PR2 = [Fosc / (Fpwm * 4 * N )] - 1
where( Tosc = 1 / Fosc ) as well as Tpwm = 1/ Fpwm

I found above equation when I study the micro controller programming myself
I can not remember now maths
so I need to subject the "PR2" from above equation
so I need the all every steps and rule I need to follow for above matter

Last edited: May 24, 2013
2. May 24, 2013

### rock.freak667

If the • are multiply, then you can just divide by each term that is being multiplied and carry across the 1 to the next side.

Basically, divide both sides of the equation by the N, 4 and so on. Then subtract 1 from both sides of the equation.

3. May 24, 2013

### PA3040

Can you please show me a step

4. May 24, 2013

### PA3040

ok

Step1 - Tpwm / 4 * TOSC * N = (PR2) - 1 ..; Is this correct?
Step2 - (Tpwm - PR2) / 4 * TOSC * N = -1 ..; Is this correct?

5. May 24, 2013

### rock.freak667

Step 1 is somewhat correct, your equation should be

$$\frac{Tpwm}{4*TOSC*N} = PR2 +1$$

Now if you subtract 1 from both sides what do you get on the left side? What is left on the right side?

6. May 24, 2013

### PA3040

Next = [ Tpwm / ( 4 * TOSC * N ) ] - 1 = PR2 + 1 - 1

now [ Tpwm / ( 4 * TOSC * N ) ] - 1 = PR2 writr?

7. May 25, 2013

### rock.freak667

That should be correct now.