find the number of terms if:2+4+6+8+......=10100

Asked by riyaliz | 22nd Jul, 2008, 10:13: PM

Expert Answer:

a = 2, d = 2

sum of n terms = n/2 [2a +(n-1)d]

10100 = n/2 [4 +(n-1)2]

10100 = 2n + n(n-1)

n2 - n + 2n -10100 = 0

n2 +n -10100 = 0

n2 + 101n -100n -10100 = 0

n(n+101) -100(n+101)=0

(n-100)(n+101)=0

n = 100 or n = -101 (negative number of terms is not possible )

n = 100

 

 

Answered by  | 23rd Jul, 2008, 09:10: PM

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