Optimization

AP Calculus AB· difficulty 4/5

The point on the parabola y=x2y = x^2 closest to (0,1/2)(0, 1/2) has x-coordinate

  • A

    1/21/2

  • B

    00

    check_circle
  • C

    ±1\pm 1

  • D

    ±2/2\pm \sqrt{2}/2

Explanation

Squared distance D=x2+(x21/2)2D = x^2 + (x^2 - 1/2)^2. D=2x+2(x21/2)(2x)=2x[1+2(x21/2)]=2x[2x2]D' = 2x + 2(x^2-1/2)(2x) = 2x[1 + 2(x^2-1/2)] = 2x[2x^2]. Zero at x=0x=0. (At x=0x=0, D=1/4D = 1/4; smaller than alternatives.)

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