сократить дробь. алгебра 10 кл

(a - 9 a^(1/2)) / (7 a^(1/4) + 21) = a^(1/2) (a^(1/2) - 9) / (7 (a^(1/4) + 3) = a^(1/2) ( a^(1/4) - 3) (a^(1/4) + 3) / (7 (a^(1/4) + 3) =
= (1/7) a^(1/2) (a^(1/4) -3) = (a^(3/4) - 3 a^(1/2)) / 7