i got read of one root but instead i got another one
??
The denominator factorises to .
Thus, The fraction becomes .
You have a sign error. is ve, and not ve. Your formula produced are correct, just a sign error has made them slightly differ.
You can continue to use gaussian elimination after you've made the correction.
Your equations are correct.
There is a much easier way :
Multiply both sides by u
And set u to 0
Multiply both sides by u+1
And set u to -1