Question

Q6. The first three terms of an arithmetic series are 60, 4p and 2p-6 respectively (a) Show that p= 9 (b) Find the value of the 20th term of this series. (c) Prove that the sum of the first n terms of this series is given by the expression 12n (6 - n)

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Answer 1

p=9

t20=516

Explanation:

a

4p-60=2p-6-2p

6p=54

p=9

b

a=60.. d=24

t20=a+19d

=60+19×24

=516

c

Sn=12.5+12.3+12.1

=12n(6-n)