# Is this correct?

• February 28th 2010, 07:48 PM
jzellt
Is this correct?
Solve 3x + 3 = x + 5 mod 11 (= is congruence not equality...)

(3x - x) = (5 - 3) mod 11
2x = 2 mod 11
2x = 13 mod 11
x = 13/2 mod 11

Is this correct?
• February 28th 2010, 08:27 PM
dani
No. To be able to divide by an element $a$ (2 in this example) you need to find $a^{-1}$ such that $a\times a^{-1}=1$. If the inverse does not exist, you cannot "divide" by $a$.

so in your example, $a=2$ and $a^{-1}=6$ ...