Answer: 8 * 10⁻⁸ cm² .
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Explanation:
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(2 * 10⁴ cm) * (4 * 10⁻¹² cm) =
2 *4 * 10⁴ * 10⁻¹² = 8 * 10⁽⁴⁺⁽⁻¹²⁾⁾ = 8 * 10⁻⁸ cm² .
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Note the follow property of exponents:
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xᵃ * xᵇ = x⁽ᵃ ⁺ ᵇ⁾ ; as such: " 10⁴ * 10⁻¹² = 10⁽⁴⁺⁽⁻¹²⁾⁾ = 10⁻⁸ " .
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