Actually, this problem is *not* that hard, provided it is two separate problems. The second one, for example, is to find U

^{-1}, where:

.

you should know (hopefully) that the product of two upper-triangular matrices with diagonal entries of 1, is another such matrix. since I (the identity matrix) is also upper triangular, with diagonal entries all 1, it seems reasonable to conjecture that U

^{-1} is also upper-triangular with 1's on the diagonal. so we want to solve THIS equation:

for x,y and z, in terms of a,b and c. you can do this.