I know how to do every part except for part d).

I know that b-Ax is perpendiular to Ax, ie, the column space of A, but how does that have to do anything with the Q?

Btw the residual vector is given by (0.40476, 0.79619, -2.51238, 0.47905, 1.37048, -0.65143) the sum is -0.11333 which is approximately 0 due to rounding etc.

is any least square solution of Ax=b

any help would be appreciated!

Thanks!