# HKDSE Mathematics Question Review (2021-01-08)

07/01/21 20:31

Given x+y=6

Find max(xy).

07/01/21 20:33

Answer,

x=y is the optimal.

So we have 2x=6

max(xy) = x^2 = 9

07/01/21 22:14

Sketch the graph for the following equation: xy-2x-2y-2=0

07/01/21 22:16

Sketch the graph for the following equation: xy-2x-2y-2=0

Answer:

It is simply factorization stuff:

(x-2)(y-2) =6

It is an rectangular hyperbola,

with translation of the origin to (2,2).