Find the twentieth term if a36 = 78 and a42 = 90

Find the twentieth term if a36 = 78 and a42 = 90

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1 Answer

a36 = 78 and a42 = 90

ak=a+(k-1)d

a36 = 78 =a+35d...............eq1

a42 = 90=a+41d.................eq2

eq2-eq1

12=6d

6d=12

d=12/6=2

78=a+35*2

78=a+70

a=8

a20=8+(20-1)2

a20=8+19*2=8+38=46

by Level 8 User (32.3k points)

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