"th" is added to the name of the negative power. Here are a few of them ...
10¹ = ten; 10⁻¹ = tenth
10² = hundred; 10⁻² = hundredth
10³ = thousand; 10⁻³ = thousandth
10⁶ = million; 10⁻⁶ = millionth
10⁹ = billion; 10⁻⁹ = billionth
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