Помогите решить систему

 

3x = y + 1 и 7^(y-2x+2) = 7^(y-4x+1) + 6

Решала подстановкой, получила y = 3x-1 и 7^(x+1) = 7^(-x) + 6

Заменив 7^x = y получила 7y = 1/y + 6

В итоге получилась пара чисел 2/3 и 1, однако с ответом не совпадает :( там (0; -1)

Подскажите, что я делаю не так

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Dmitri Mendeleev is a great Russian scientist of the 19th century. He _____ as a great chemist who _____ the periodic classification of the elements Dmitri Mendeleev was born in Tobolsk in 1834.At school,Dmitri_____ in mathematics,physics,and geography but was not good at languages.In 1855 he graduated from the Pedagogical Institute in St Petersburg with a goid medal for his____.In 1856 , he_____in chemistry. Dmitri Mendeleev's contribution to the world's science was_____. He was the first____the dependence of the qualities of the elements on their atomic weight.He forecast that the gaps in the table of elements would be filled in by elements which______yet.Dmitri Mendeleev was greatly honoured as a _____ of academies in many countries.Element No 101 _____ him. It is called Mendelevium.

Слова:

Achievement
create
enormous
member
name after
not discover
receive a degree
research
succeed

Твір на тему Суботник,будь ласка допоможіть дуже срочно потрібно?твір повинен бути на 2 сторінки,дякую)

Упростите выражение.
(1/mn+1/m+n)×m^2-n^2/m

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