If 5^x = 1/3, then 5^−7x = ?

If x² + 1/x² = 51, then (x − 1/x) is equal to

If 2^(2x−1) + 4^x = 2^(x−1/2) + 2^(x+1/2), then the ratio (1−x)/(1+x) is

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

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

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