SOLUTION: The 4th term of an AP is zero. Prove that the 25th term of the A.P. is three times the 11th term.

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Question 1088296: The 4th term of an AP is zero. Prove that the 25th term of the A.P. is three times the 11th term.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a%5B4%5D=a%5B1%5D%2B%28n-1%29d=a%5B1%5D%2B3d=0
So,
a%5B1%5D=-3d
and
a%5B25%5D=a%5B1%5D%2B%2825-1%29d
a%5B25%5D=-3d%2B24d
a%5B25%5D=21d
and
a%5B11%5D=a%5B1%5D%2B%2811-1%29d
a%5B11%5D=-3d%2B10d
a%5B11%5D=7d
So then,
a%5B25%5D=21d
a%5B25%5D=3%287d%29
a%5B25%5D=3%2Aa%5B11%5D