Mathematics

Mathematics

Problem

The equation x2+y2+z2+4x−6y+2z+9=0x^2+y^2+z^2+4x-6y+2z+9=0 represents a sphere. What are the coordinates of its centre? a) (−4,6,−2)(-4,6,-2) b) (2,−3,1)(2,-3,1) c) (−2,3,−1)(-2,3,-1) d) (−2,3,1)(-2,3,1)
Intuitive explanation

To find the center of a sphere, you need to rewrite the equation in standard form (x−h)2+(y−k)2+(z−l)2=r2(x-h)^2+(y-k)^2+(z-l)^2=r^2 by completing the square for each variable. The key insight is that the linear terms 4x4x, −6y-6y, and 2z2z tell you exactly what to add and subtract—match each pair of terms to a perfect square, and the constants inside those squares reveal the center coordinates directly.

Intuitive explanation

To find the center of a sphere, you need to rewrite the equation in standard form (x−h)2+(y−k)2+(z−l)2=r2(x-h)^2+(y-k)^2+(z-l)^2=r^2 by completing the square for each variable. The key insight is that the linear terms 4x4x, −6y-6y, and 2z2z tell you exactly what to add and subtract—match each pair of terms to a perfect square, and the constants inside those squares reveal the center coordinates directly.

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