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#### Technology 4 ESO – Unit 4 ORTHOGRAPHIC DRAWING extra activities

An arithmetic sequence is a sequence of numbers such that the difference of any two successive numbers of the sequence is a constant.

1. a) Watch the video on “Arithmetic sequences and series” and answer:
• I)  What number is n3 in the sequence?
• II)  What is “d”?
• III)  What is the value of “d”?
• IV)  Use the formula in the video to find a50 (the 50th term of the sequence).
• V)  What would be the value of a50 if the difference was 6?

b) Watch the video on “Is A Number In A Sequence” and answer:

• I)  Is “43” a term in the sequence “2n + 4”? Why?
• II)  Is “95” a term in the sequence “3n – 1”? Why?

A geometric sequence is a sequence of numbers that follows a pattern were the next term is found by multiplying by a constant called the “common ratio”, r.

c)  Watch the video on “Geometric sequences and series” and answer:

• I)  What is a geometric sum?
• II)  What three things do we need to know to solve a geometric sum?
• III)  Using the formula, find S8        (Sn for n=8 , the sum of the first 8 terms of the sequence).
• IV)  Use the formula to find S20
• V)  What would be the value of S20 if r=3 ?

d) Watch the video on “How to find the first four terms of a sequence” and answer:

• I)  Why is the series an “alternate sign” series?
• II)  Find a12