1. A department store has found that its value of sales (z) depends on the number of advertisements in circulars (x) and in newspapers (y), given by z = 420x – 2x2 – 3xy – 5y? + 640y + 1725. If the...

Extracted text: 1. A department store has found that its value of sales (z) depends on the number of advertisements in circulars (x) and in newspapers (y), given by z = 420x – 2x2 – 3xy – 5y? + 640y + 1725. If the price per advertisement is RM1 in circulars and RM4 in newspapers, and the advertising budget is RM180, iii) Use the Bordered Hessian to show that the sales are in fact a maximum. iv) Estimate the effect on sales of a $1 increase in the advertising budget. Provide your comment.