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# x=?

0
459
1

x^0,5+x²=17

18.04.2017

#1
+102447
+2

$$x ^ {0.5} + x^2 = 17\\ x ^ {0.5} + (x ^ {0.5} )^4 = 17\\ let\;\;t=x ^ {0.5} \\ t+t^4=17\\ t^4+t-17=0$$

This has at most 4 real answers.

If I graph $$y=x^4+x-17$$

and see where it crosses the x axis that will be the solutions.

So t might equal 1.969   or   -2.09

$$t=x^{0.5}\\ t^2=x\\ If\;\;t=1.969,\quad x=3.877\\ LHS=3.877^{0.5}+3.877^2=21.2\ne RHS\\~ \\If\;\;t=-2.09,\quad x=4.368\\ LHS=4.368^{0.5}+4.368^2=17=RHS\\~$$

So I get   x= 3.877      Correct to 3 decimal places

I am going to enter this into WolframAlpha to see if our answers are the same.

https://www.wolframalpha.com/input/?i=x%5E+0.5+%2B+x%5E2+%3D+17