Determine the centre and radius of a circle whose equation is 1/2x(4x-8)+ 1/4y(8y−12)=24

Mathematics

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Answer

The center of the circle is (1,3/4)(1, 3/4) and the radius is sqrt(217) / 4.

Step-by-step solution

5 steps

Here are the steps to determine the center and radius:

  1. Expand and simplify the given equation

    The equation is 1/2x(4x−8)+1/4y(8y−12)=241/2x(4x-8) + 1/4y(8y-12) = 24.
    Expand the terms:
    (1/2x)(4x)−(1/2x)(8)+(1/4y)(8y)−(1/4y)(12)=24(1/2x)(4x) - (1/2x)(8) + (1/4y)(8y) - (1/4y)(12) = 24
    2x2−4x+2y2−3y=242x^2 - 4x + 2y^2 - 3y = 24

  2. Divide by the coefficient of x² and y² to make them 1

    Divide the entire equation by 2:
    x2−2x+y2−(3/2)y=12x^2 - 2x + y^2 - (3/2)y = 12

  3. Rearrange terms and complete the square for x and y

    Group the x-terms and y-terms:
    (x2−2x)+(y2−(3/2)y)=12(x^2 - 2x) + (y^2 - (3/2)y) = 12

    To complete the square for x2−2xx^2 - 2x, take half of the coefficient of x (-2), which is -1, and square it (−1)2=1(-1)^2 = 1.
    To complete the square for y2−(3/2)yy^2 - (3/2)y, take half of the coefficient of y (-3/2), which is -3/4, and square it (−3/4)2=9/16(-3/4)^2 = 9/16.

    Add these values to both sides of the equation:
    (x2−2x+1)+(y2−(3/2)y+9/16)=12+1+9/16(x^2 - 2x + 1) + (y^2 - (3/2)y + 9/16) = 12 + 1 + 9/16

  4. Rewrite in standard form of a circle (x-h)² + (y-k)² = r²

    (x−1)2+(y−3/4)2=13+9/16(x - 1)^2 + (y - 3/4)^2 = 13 + 9/16

    Calculate the right side:
    13+9/16=(13⋅16)/16+9/16=208/16+9/16=217/1613 + 9/16 = (13 \cdot 16)/16 + 9/16 = 208/16 + 9/16 = 217/16

    So the equation in standard form is:
    (x−1)2+(y−3/4)2=217/16(x - 1)^2 + (y - 3/4)^2 = 217/16

  5. Identify the center and radius

    Comparing this to (x−h)2+(y−k)2=r2(x-h)^2 + (y-k)^2 = r^2:
    The center (h, k) is (1,3/4)(1, 3/4).
    The radius squared r2r^2 is 217/16217/16.
    The radius rr is sqrt(217/16) = sqrt(217) / sqrt(16) = sqrt(217) / 4.

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