SOLUTION: Find the real solutions of the equation. This one threw me into a loop. 4x^(1/2) - 9x^(1/4) + 4 = 0

Algebra ->  Radicals -> SOLUTION: Find the real solutions of the equation. This one threw me into a loop. 4x^(1/2) - 9x^(1/4) + 4 = 0      Log On


   



Question 1207659: Find the real solutions of the equation.

This one threw me into a loop.

4x^(1/2) - 9x^(1/4) + 4 = 0

Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
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Find the real solutions of the equation.
4x^(1/2) - 9x^(1/4) + 4 = 0
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Introduce new variable  y = x^(1/4).

Then our original equation takes the form

    4y^2 - 9y + 4 = 0.


It is a quadratic equation for y.  Solve it using the quadratic formula

    y%5B1%2C2%5D = %289+%2B-+sqrt%28%28-9%29%5E2+-+4%2A4%2A4%29%29%2F%282%2A4%29 = %289+%2B-+sqrt%2881-64%29%29%2F8 = %289+%2B-+sqrt%2817%29%29%2F8.


Thus, there are two real roots for y:  y= %289+%2B+sqrt%2817%29%29%2F8  and  y= %289+-+sqrt%2817%29%29%2F8.


It gives two real positive solutions for x

    x = y^4 = %28%289+%2B+sqrt%2817%29%29%2F8%29%5E4 = 7.240799963  (approximately).

and

    x = y^4 = %28%289+-+sqrt%2817%29%29%2F8%29%5E4 = 0.138106287  (approximately).

Solved.

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Again, the method of solution is changing the variable.