- 412

- 2

**[SOLVED] Maximum value of xy**

**1. Homework Statement**

Q] Given that [itex]x \in [1, 2][/itex] and [itex]y \in [-1, 1][/itex] and [itex]x + y = 0[/itex], find the maximum value of [itex]xy[/itex]

**3. The Attempt at a Solution**

I have no idea at all. Does this have something to do with the maxima/minima. In that case, i can get that:

[tex]

\frac{dx}{dy} = xdy + ydx

[/tex]

also,

[tex]

dx = -dy

[/tex]

hence, for the condition of [itex]f'(x) = 0[/itex],

[tex]

xdy + ydx = 0

[/tex]

[tex]

xdy = - ydx

[/tex]

[tex]

\frac{dy}{dx} = \frac{-y}{x}

[/tex]

i don't even know what i'm doing till now.