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The following problem refers to a geometric sequence. If a_1=-2 and r=-1. Find a_20.

a_n=a_1*r^(n-1)
a_20=-2*-1^(20-1)
I am stuck now please help me.

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So you have (-2) times by (-1)^19
= (-2) we know that it is -1 times by itself 19 times... so just -1
= and you figure out the rest : )

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