Question

Dada a PA ( 24,21,... ) Calcule a) a1=
b)r=
c)a15=
d)a50=
e)a20=

Answer 1

a)

a1 = 24

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b)

r = a2 - a1

r = 21 - 24

r = -3

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c)

an = a1 + ( n -1 ) . r

a15 = 24 + ( 15 -1 ) . ( -3 )

a15 = 24 + ( 14 ) . -3

a15 = 24 - 42

a15 = -18

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d)

an = a1 + ( n -1 ) . r

a50 = 24 + ( 50 -1 ) . ( -3 )

a50 = 24 + ( 49 ) . -3

a50 = 24 - 147

a50 = -123

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e)

an = a1 + ( n -1 ) . r

a20 = 24 + ( 20 -1 ) . ( -3 )

a20 = 24 + ( 19 ) . -3

a20 = 24 - 57

a20 = -33