Question

For what value of p are 2 1, 7 and 3p three consecutive terms of an ap.

Answer 1

as we know d =a2-a1 and d is also equal to a3-a2
a2-a1= 7-21= - 14 which means d= -14

therefore a3-a2= - 14
3p-7= - 14
3p = -14 + 7
3p= -7
p= -7/3

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