Sum of A.P 7+11+15+........+x=168.find x?
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a=7
d= 11-7=4
we know that
Sn= n/2 ( 2a +(n-1) d)
Sn=n/2 ( 2×7+(n-1) 4)
168=n/2 ( 14 +4n-4)
168= n/2 ( 10 +4n)
168×2= ( 10+4n)
336 = (10 +4n)
336 - 10= 4n
326 = 4n
326 /4 = n
a=7
d= 11-7=4
we know that
Sn= n/2 ( 2a +(n-1) d)
Sn=n/2 ( 2×7+(n-1) 4)
168=n/2 ( 14 +4n-4)
168= n/2 ( 10 +4n)
168×2= ( 10+4n)
336 = (10 +4n)
336 - 10= 4n
326 = 4n
326 /4 = n
khushi1037:
thanks a lot
plzz Mark it as brainlist answer plzz
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