How many terms of AP 24,21,18....must be taken so that their sum is 78.Explain the double answer
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3
Answer:
-17
Step-by-step explanation:
we have,
a= 24
d= a2-a= 21-24 = -3
n=?
an=78
=>a+(n-1)d=78
=>24+(n-1)(-3)=78
=>(n-1)(-3)= 78-24
=>n-1 = 54/(-3)
=>n-1= -18
=> n= -18+1
=>n= -17
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