Раскроем скобки, упростим и докажем тождество:
(5х/(х - 10) + 20х/(х^2 - 20х + 100) : (4х - 24)/(х^2 - 100) - 25х/(х - 10) = 5х/4;
1) 5х/(х - 10) + 20х/(х^2 - 20х + 100) = 5х/(х - 10) + 20х/(х - 10)^2 = (5х * (х - 10))/(х - 10)^2 + 20х/(х - 10)^2 = (5х^2 - 50х + 20х)/(х - 10)^2 = (5х^2 - 30х)/(х - 10)^2;
2) (5х^2 - 30х)/(х - 10)^2 : (4х -24)/(х^2 - 100) = (5х * (х - 6) * (х^2 - 100))/((х- 10)^2 * 4 * (х - 6)) = (5х * (х - 10) * (х + 10))/(4 * (х - 10)^2) = (5х * (х + 10))/(4 * (х - 10));
3) (5х * (х + 10))/(4 * (х - 10)) - 25х/(х - 10) = (5х^2 + 50х - 25х * 4)/(4 * (х - 10)) = (5х^2 - 50х)/(4 * (х - 10) = (5х * (х - 10)/(4 * (х - 10)) = 5х/4.