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Find the value of x when …

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Find the value of x when Ap given below 2+6+10+...+x = 1800
  • 1 answers

Gaurav Seth 6 years, 5 months ago

2 + 6 + 10 + ...... x = 1800 

here ; 2, 6, 10 , .....x are in arithematic progression where 2 is first term and 4 is common difference of ap.

use formula,  to find number of terms in ap.

x = 2 + (n - 1) × 4 

x = 2 + 4n - 4 

x = 4n - 2 

x + 2 = 4n 

n = (x + 2)/4 

now, use formula, 

here, 

1800 = {(x + 2)/4}/2 [2 + x ] 

1800 = (x + 2)/8 × (x + 2) 

1800 × 8 = (x + 2)² 

14400 = (x + 2)² 

(120)² = (x + 2)² 

x + 2 = 120 => x = 118

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