We know that
0
1 = x
/
| 1 dx
/
/ 0
= | x . dx
/
/ 0
= | x . 1 dx
/

(Here f(x) is x and 0 is its power, derivative of x is 1 which is also exist in front of x. So apply the rule take its power with plus 1 as power and divide by new power.)

0 + 1
x
= ------- + C
0 + 1
1
x
= ----- + C
1
= x + C