Need help for formuar

[PA3040D]

This is the equation - l = a + ( n - 1 ) d

I subject " n" in two way but result is different , I can't understand the error in second method
please advice
please check the image attached

 

[Harry_the_cat]

The bottom line of the first method should be +d on the top.
If you change 1 to d/d on the bottom line of the second method and express with one denominator, it will be the same.

 

[PA3040D]

The bottom line of the first method should be +d on the top.
If you change 1 to d/d on the bottom line of the second method and express with one denominator, it will be the same.

The bottom line of the first method should be +d on the top.

Yes....my mistake

If you change 1 to d/d on the bottom line of the second method and express with one denominator, it will be the same.

Yes agreed . Can you prove it , we can't simply change it without proved

I mean...the letter should coming from the equation itself


please advice

 

[Harry_the_cat]

1 = d/d so you are not changing anything.

You are just getting a common denominator so you can add all the terms.

 

[lev888]

Yes agreed . Can you prove it , we can't simply change it without proved

There is nothing to prove. This is how you add a fraction and a number: ${\displaystyle \frac{a}{b}+c=\frac{a}{b}+\frac{cb}{b}=\frac{a+cb}{b}}$

 

[Steven G]

$$\dfrac {l-1}{d} + 1 = \dfrac{l-1}{d} + \dfrac{d}{d} = \dfrac{l-1+d}{d}$$
How can you be able to do all that work but not know how to get common denominators?