Question

how many terms of the sequence 18,16,14... should be taken, so that their sum is 78? explain double answer.​

Answer 1

Answer:

hey mate

here u go

Step-by-step explanation:

AP : 18, 16, 14, 12

Common difference,d = 16-18= -2

Sn= 78

n/2{2a+(n-1)d}=78

n/2{2(18)+(n-1)(-2)}=78

n/2{36-2n+2}=78

n/2{38-2n}=78

19n - n sq. = 78

-n square + 19n - 78 =0

n(-n+13)-6(n+13)=0

(-n+13)(n-6)=0

-n+13=0 or n-6=0

n=6,13

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