Verify the equation ∫ cos 2xdx = 1 / 2 sin 2x + C

Verify the equation ∫ cos 2xdx = 1 / 2 sin 2x + C

(1/2sin2x+C)'
=1/2*cos2x*2
=cos2x
So right

From the equation 3x-5 = 2x + 6, the deformation of x = 11 is () a divide by 3 on both sides of the equation, B add 5 on both sides of the equation, C add (2x-5) on both sides of the equation, D subtract (2x-5) on both sides of the equation

3x-2x=6+5

The following is Xiaoming's deformation process of equation 3x-2 = 2x-2, 3x-2 = 2x-2 + 2 = 2x-2 + 2, ① 3x = 2x, ② 3 = 2, ③ the basis of Xiaoming's deformation in step ①
The surface is the process of Xiao Ming's transforming the equation 3x-2 = 2x-2
3x-2=2x-2
3x-2+2=2x-2+2 ①
3x=2x ②
3=2 ③
(2) What is Xiaoming's mistake_________ Step, the reason for the mistake is__________
(3) Please write the correct solution
I'm not very good at learning

3 wrong, X may be 0, so both sides cannot be divided by X at the same time
3x-2=2x-2
3x-2x=0
x=0

A student transforms the equation 3x-2y = 2x-2y, adds 2Y to both sides, and gets 3x = 2Y. Then divide both sides by X, and the result is 3 = 2. What's the matter? Please help the student analyze the cause of the error

Add 2Y to both sides
3x=2x
The solution is x = 0
0 can't be the denominator. When dissolving, you can't directly divide both sides at the same time