X + 9 = 7
How do you move the constant to the right side and change it’s sign

X + 9 = 7
You can throw the X to the right side and change to -X
9 = 7 - X
OR You can add both sides with -X
X + 9 - X = 7 - X
9 = 7 - X
Then you can do the same with 7 by throwing it to the left side and get -7
9 - 7 = - X
2 = - X
Now throw the -1 to the left side ( -X = -1X )
2(-1) = X
X = -2