We're stuck on this for too long now.
How do you properly solve these questions? We've tried to make sense of the solution but couldn't figure it out.
Ill include my approach to Problem 8, probably the approach for Problem 7 is the same?
You'd save lives.
Thanks a lot!
For problem 8, look at this, it's quite straightforward ! :-)
It's better if use the definition of the matrix product on a generic matrix W. For example on problem 7
For problem 7, memorize the formula : d/dx (x_TAx) = (A_T + A)x. Then you replace A by W_TW and the result is easy to find.