maksimumkan f(r,s) = r^2 - 10s^2 terhadap r-s=18

jawab

misal y = r² -10s²

r - s = 18
r = 18 + s

y = (18 + s)²  - 10 s²
y = 324 + 36s + s² -10s²
y = 324 + 36s - 9s²

y' = 0
36 - 9 s= 0
s = 4
r = 18 + s
r = 22

f(r.s)= f(22, 4) = (22)²- 10(4)²
f(r.s) = 484 - 160
f(r,s) = 324