Đáp án:
`x=2000`
Giải thích các bước giải:
$\\$
`(1909 - x)/91 + (1907-x)/93 + (1905-x)/95 + (1903-x)/97 + 4=0`
`⇔ ( (1909-x)/91 + 1) +( (1907-x)/93 + 1) + ( (1905-x)/95 + 1) + ( (1903-x)/97+1)=0`
`⇔ ( (1909-x)/91 + 91/91) + ( (1907-x)/93 + 93/93) + ( (1905-x)/95 + 95/95) + ( (1903-x)/97 + 97/97) =0`
`⇔ (1909-x + 91)/91 + (1907-x+93)/93 + (1905-x+95)/95 + (1903-x+97)/97=0`
`⇔ ((1909+91)-x)/91 + ( (1907+93)-x)/93 + ( (1905+95)-x)/95 + ( (1903+97)-x)/97=0`
`⇔ (2000-x)/91 + (2000-x)/93 + (2000-x)/95 + (2000-x)/97=0`
`⇔ (2000-x) (1/91 + 1/93 + 1/95 + 1/97) = 0` `(1)`
Ta thấy : `1/91 \ne 0,1/93 \ne 0, 1/95 \ne 0, 1/97 \ne 0`
`⇒ 1/91 + 1/93 + 1/95 + 1/97 \ne 0`
Nên từ `(1)`
`⇔2000-x=0`
`⇔x=2000-0`
`⇔x=2000`
Vậy `x=2000`