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9. If the 3rd and the 9th terms of an AP are 4 and - 8 respectively, which term of this AP is zero?​

Answer»

let the 1st term is a and common difference is bso a+(3-1)b=4a+2b=4, a=4-2b again,a+(9-1)b= -8a+8b= -8, a= -8-8b 4-2b= -8-8b -2b+8b= -8-46b= -12B= -12/6= -2a=4-2b=4-2.(-2)=4+4=8let the NTH term is 0a+(n-1)b=08+(n-1)(-2)=08-2n+2=02n=10n=10/2=55th term of this AP is ZERO


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