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

1.	Find the value of x when Ap given below 2+6+10+...+x = 1800
Answer» 2 + 6 + 10 + ...... x = 1800\xa0here ; 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\xa0x = 2 + 4n - 4\xa0x = 4n - 2\xa0x + 2 = 4n\xa0n = (x + 2)/4\xa0now, use formula,\xa0here,\xa01800 = {(x + 2)/4}/2 [2 + x ]\xa01800 = (x + 2)/8 × (x + 2)\xa01800 × 8 = (x + 2)²\xa014400 = (x + 2)²\xa0(120)² = (x + 2)²\xa0x + 2 = 120 => x = 118

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