X + 7y = 5
3x - y = 81 /*7
x + 7y = 5
21x - 7y = 567
------------------------- +
22x = 572
x = 26
y = 3x - 81 = - 3
Ответ
(26 ; - 3)
50^n+1 / 2^n-3 * 5^2n+1 = (25*2)^n+1 / 2^n-3 * 5^2n+1 = 25^n+1 * 2^n+1 / 2^n-3 * 5^2n+1 =
=(5^2)^n+1 * 2^n+1 / 2^n-3 * 5^2n+1= 5^2(n+1) * 2^n+1 / 2^n-3 * 5^2n+1 = 5^2n+1 * 2^n+1 / 2^n-3 * 5^2n+1 = 5^ 2n+2-(2n+1) * 2^n+1-(n-3) = 5^1 * 2^4=5*16=80