Answer:
See below.
Step-by-step explanation:
1) Two equations are equivalent if they have the same solutions.
2) As long as two expressions [tex]a[/tex] and [tex]b[/tex] are equal, so [tex]a=b[/tex], adding the same value for both sides still makes the equation true, so
[tex]a = b[/tex]
[tex]a + c = b + c[/tex] is true.
3) As long as two expressions [tex]a[/tex] and [tex]b[/tex] are equal, so [tex]a=b[/tex], subtracting the same value for both sides still makes the equation true, so
[tex]a = b[/tex]
[tex]a - c = b - c[/tex] is true.
