20/(х+20)+20/(20-х)+25/60=2 1/2

20/( Х + 20 ) + 20/( 20 - Х ) + 25/60 = 2 1/2
( 20( 20 - Х ) + 20( Х + 20 )) /( 400 - х^2 ) = 5/2 - 5/12
( 400 - 20х + 20х + 400 )/ ( 400 - х^2 ) = 30/12 - 5/12
800/( 400 - х^2 ) = 25/12
800•12 = 25( 400 - х^2 )
32•12 = 400 - х^2
384 = 400 - х^2
Х^2 = 16
Х1 = 4
Х2 = - 4
Ответ 4 ; - 4