Question

7^2x+1 + 4*21^x = 3^2x+1

Answer 1

(7*7^2x+4*7^x*3^x = 3^2x*3 ) / 3^2x
7*(7/3)^2x+4*(7/3)^x = 3        (7/3)^x = a
7a^2+4a-3 = 0