When you have an exponent that is negative, it means to take reciprocal of the fraction then take it the power.
Some examples:
5^-2 = 1/5^2 = 1/25
10^-3 = 1/10^-3 = 1/1000
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I think 1 because if you had 2 you'll end up with a shape that is greater than 180 degrees. Keep in mind obtuse angles a over 90 degrees. hope that helped
16 can be expressed as a difference of two prime numbers in two ways, which
is:23 - 7 = 16, 19 - 3 = 16
Among the choices, 16 is expressed as (23 - 7), which is the difference of two prime numbers.