Question

Find the first negative term of an AP series 55 , 50 , 45 ,40 ,..?

Answer 1

Here , a=55

d=55-50= -5

Let the n^th term of the given AP be the first negative term .

Then ,\(a_n<0\) 

\(=( {a+(n-1)d} )<0\)

\(=( {55+(n-1)(-5)} )<0\)

\(=( 55-5n+5)<0\)

\(=60-5n<0\)

\(=60<5n\)

\(=5n>60\) 

\(=n>12\) 

\(\therefore n=13\)

Hence , the 13th term is the first negative term of the given AP

 

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