a·(x^7 + 1) + b·x^7 = c
a·x^7 + a + b·x^7 = c
a·x^7 + b·x^7 = c - a
x^7·(a + b) = c - a
x^7 = (c - a) / (a + b)
x = ((c - a) / (a + b))^(1/7)
a·(x^7 + 1) + b·x^7 = c
a·x^7 + a + b·x^7 = c
a·x^7 + b·x^7 = c - a
x^7·(a + b) = c - a
x^7 = (c - a) / (a + b)
x = ((c - a) / (a + b))^(1/7)