PLEASE DO NOT PUT BEFORE ANSWER!!! It is WRONG!

I need to prove the case and I will put the theorem.

A is a tridiagonal matrix. I need to do Gauss elimination and then by using assumption in the case to show all d's are positive then A is invertible.

THEOREM: Suppose A is tridiagonal and all off-diagonal entries are non zero. If (dil >= |ci|+|ei| (2 == |e1| and|dn| > |cn| or|d1| > |e1 and |dn| >= |cn| then A is invertible. CASE: |d1>= |e11 |d2| >= |c2|+|e2| |d3| >= |c3|+|e3|, |d4| > |c4|. Prove that A is invertible. THEOREM: Suppose A is tridiagonal and all off-diagonal entries are non zero. If (dil >= |ci|+|ei| (2 == |e1| and|dn| > |cn| or|d1| > |e1 and |dn| >= |cn| then A is invertible. CASE: |d1>= |e11 |d2| >= |c2|+|e2| |d3| >= |c3|+|e3|, |d4| > |c4|. Prove that A is invertible