Solve x^(1/2)-(81x)^(1/4)-4=0

Question

x^(1/2)-3(x)^(1/4)-4=0

Answer 1

If you let u = x^(1/4) your equation becomes much easier to look at:

x^(1/2)-3x^(1/4)-4 = 0
u^2 - 3u - 4 = 0

solve for u, and then x = u^4