Multivariate calculus problem?

Find the absolute maximum and minimum of the function f(x,y)=x^2+2y^2-2y on the closed disc x^2+y^2 (less than/equal to) 5.

Please explain in detail, thanks!

Comments

  • If there's an extremum in the interior of the region, it will occur at a critical point.

    ∇f = 2x i + (4y - 2) j = <0, 0> ==> x = 0 and y = 1/2.

    The point (0, 1/2) is inside the circle.

    On the boundary,

    f(x, y) = x² + 2y² - 2y = (x² + y²) + y² - 2y = y² - 2y + 5 = (y - 1)² + 4,

    and -√5 ≤ y ≤ √5. The minimum value of this occurs at the vertex where y = 1 and f = 4. The maximum occurs at y = -√5 where f = 10 + 2√5

    f(0, 1/2) = -1/2 <----absolute minimum

    f(±2, 1) = 4

    f(0, -√5) = 10 + 2√(5) <----absolute maximum

  • a million) vital of x^2 y dydx = x^2 * y^2/2 for 2 < y < 4: x^2 * (sixteen/2 - 4/2) = 6x^2 vital of 6x^2 dx = 6x^3/3 = 2x^3 for 0 < x < a million: 2(a million)^3 - 0 = 2 no longer 3. 2) y = x/2 -and- y = sqrt(x) x^2/4 = x, x = 0 & 4 Integrating (sqrt(x) - x/2) dx for x = 2 to 4: 2/3 x^(3/2) - x^2/4. Plug in 4 & 2 and spot what you get. 3) ultimate. person-friendly to make certain with out calculus - that is one sector of a unit circle, so it may be pi/4.

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