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What happens to a negative component when calculating vector magnitude?

When calculating vector magnitude, a negative component is squared, which results in a positive value. This ensures that the direction indicated by the negative sign (e.g., downward or leftward) does not reduce the overall length of the vector. The magnitude depends on the absolute size of the displacement, not its direction.

Conditions

  • The vector has real components in a Cartesian coordinate system.
  • The magnitude is computed using the Euclidean formula x2+y2\sqrt{x^2 + y^2}.

Reasoning, step by step

  1. Identify the negative component (e.g., y=−3y = -3).
  2. Substitute it into the magnitude formula: x2+(−3)2\sqrt{x^2 + (-3)^2}.
  3. Square the negative component: (−3)2=9(-3)^2 = 9.
  4. Add this positive value to the square of the other component.
  5. Take the square root of the sum.

Example

For a⃗=(5,−3)\vec{a}=(5,-3), the term (−3)2(-3)^2 becomes 99. The magnitude is 25+9=34\sqrt{25+9} = \sqrt{34}, not 25−9\sqrt{25-9}.

Common misconceptions

  • Thinking that a negative component subtracts from the magnitude.
  • Confusing the direction of the component with its contribution to the length.

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