 Arithmetic and Geometric Sequences

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Arithmetic and Geometric Sequences

Arithmetic Sequences Every day a radio station asks a question for a prize of \$150. If the 5th caller does not answer correctly, the prize money increased by \$150 each day until someone correctly answers their question.

Arithmetic Sequences Make a list of the prize amounts for a week (Mon - Fri) if the contest starts on Monday and no one answers correctly all week.

Arithmetic Sequences Monday : \$150 Tuesday: \$300 Wednesday: \$450
Thursday: \$600 Friday: \$750

Arithmetic Sequences These prize amounts form a sequence, more specifically each amount is a term in an arithmetic sequence. To find the next term we just add \$150.

What is an arithmetic sequence?
A sequence in which each term is found by ADDING the same number to the previous term. 4, 8, , 16, 20………….. +4 +4 +4 +4

What is the common difference?
The difference between each number. This determines what is added to each previous number to obtain the next number. 4, 8, 12, 16, 20………….. 4 is the common difference

Geometric Sequence What if your pay check started at \$100 a week and doubled every week. What would your salary be after four weeks?

GeometricSequence Starting \$100. After one week - \$200
After two weeks - \$400 After three weeks - \$800 After four weeks - \$1600. These values form a geometric sequence.

What is a geometric sequence?
A sequence in which each term can be found by multiplying the previous term by the same number. 3, 9, , 81, ………….. x3 x3 x3 x3

What is the common ratio?
The number used to multiply by each previous number to obtain the next number. 2, 8, 32, 128, 512………….. 4 is the common ratio

Let’s Practice!

Is this an arithmetic or geometric sequence?
10, 15, 20, 25, 30…… Arithmetic Sequence +5 5 is the common difference

Is this an arithmetic or geometric sequence?
2, 12, 72, 432, 2,592…… Geometric Sequence x6 6 is the common ratio

What is the next term in this sequence? 5, 20, 80, 320 , _____
Is this an arithmetic or geometric sequence? What is the common ratio or difference? What is the next term in this sequence? 5, 20, 80, 320 , _____ x4 x4 x4 x4 1,280

What is the next term in this sequence? 5, -1, -7 -13 , _____
Is this an arithmetic or geometric sequence? What is the common ratio or difference? What is the next term in this sequence? 5, -1, , _____ -6 -6 -6 -6 -19

What is the next term in this sequence? -3, 6, -12, 24 , _____
Is this an arithmetic or geometric sequence? What is the common ratio or difference? What is the next term in this sequence? -3, 6, -12, 24 , _____ X-2 X-2 X-2 X-2 -48

What is the next term in this sequence? -400,-380,-360,-340 , ____
Is this an arithmetic or geometric sequence? What is the common ratio or difference? What is the next term in this sequence? -400,-380,-360,-340 , ____ +20 +20 +20 +20 -320

What is the next term in this sequence? 100, 75, 50 , 25____
Is this an arithmetic or geometric sequence? What is the common ratio or difference? What is the next term in this sequence? , 75, 50 , 25____ -25 -25 -25 -25

What is the next term in this sequence? 12, -48, 192 , -768____
Is this an arithmetic or geometric sequence? What is the common ratio or difference? What is the next term in this sequence? 12, -48, 192 , -768____ x-4 x-4 x-4 x-4 3,072