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# ​ What is ∑n=16[4(−5)n−1] equal to?

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What is ∑n=16[4(−5)n−1]∑n=16[4(−5)n−1] equal to?

May 16, 2018

#1
+972
+2

Hey Hev!

When n = 1,

$$4(-5)^{1-1}=4(-5)^0=4\cdot1=4$$

When n = 2,

$$4(-5)^{2-1}=4(-5)^1=4\cdot-5=-20$$

When n = 3,

$$4(-5)^{3-1}=4(-5)^2=4\cdot25=100$$

We can tell there is a pattern with multiplying by -5.

The next three terms in order are -500, 2500, and -12500

You add them to find the solution,

I hope this helped,

Gavin

May 16, 2018

#1
+972
+2

Hey Hev!

When n = 1,

$$4(-5)^{1-1}=4(-5)^0=4\cdot1=4$$

When n = 2,

$$4(-5)^{2-1}=4(-5)^1=4\cdot-5=-20$$

When n = 3,

$$4(-5)^{3-1}=4(-5)^2=4\cdot25=100$$

We can tell there is a pattern with multiplying by -5.

The next three terms in order are -500, 2500, and -12500

You add them to find the solution,

I hope this helped,

Gavin

GYanggg May 16, 2018