Question

I NEED HELP WITH PRECALC PLEASE

Answer 1

1. (d) 2 +(-5) +(-12) +...
2. (a) a8

Explanation:

1.

Putting n = 0 and n = 1 into the expression being summed will show you which series is correct.

2 -7n for n=0 is 2 -7·0 = 2

2 -7n for n=1 is 2 -7·1 = -5

The series of the last choice (d) is correct.

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2.

The given sequence is exponential with a first term of 3 and a common ratio if -5. Then the n-th term is ...

an = 3(-5)^(n -1)

We want to find n for an = -234,375.

-234375 = 3(-5)^(n-1)

-78125 = (-5)^(n-1)

For n to be a real number, we must have n even. In that case, the value of n is equivalent to the value that is the solution to ...

78125 = 5^(n -1)

Taking logs of both sides, we get ...

log(78125) = (n -1)·log(5)

log(78125)/log(5) = n -1 . . . . . . . . . . . . divide by log(5)

n = 1 +log(78125)/log(5) = 1 +7 = 8 . . . add 1 and evaluate

-234,375 is the 8th term of the sequence.

Answer 2

Answer: First question: D, Second question: A

Explanation:

Note: I'm not so good at expanding so I'll just solve it :)

So this leaves either C or D

Apply the sum rule:

8-70=-62

The only one that gives a negative sum is D

For the second picture, the one you have chosen is correct

a1 = 3 and r = -5 so:

an = 3/5 * (-5)^n

Plugging in 8 for n (the first choice) we get the given term: -234,375