If a²−b²=17, a>b, possible value of a²+b²−ab?

If x + (1/y) = 1 and y + (1/z) = 1, then the value of z + (1/x) is

If x + 1/x = k and x² + 1/x² = k, then values of k are

If x^3 – y^3 = 117/8 and x – y = 3/2 then the value of x^2 + xy + y^2 will be

If 2^(x−1) + 2^(x+1) = 1280, then the value of x²+9x is

If a, b, c, d, e and f satisfy 2a = 3b = 6c = 9d = 12e = 18f, then what is the value of (a + b)/(c + d + e + f)?