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If x=2+√3, find the value of x²+1/x²

Sagot :

crisforp
x²+1/x² = [tex] (x + 1/x)^{2} [/tex] - 2 * x * ( 1 / x) = ( 2 + √3 + 2 - √3)^2 - 2 = 16 - 2 = 14.
kate200468
[tex]x^2+ \frac{1}{x^2} =x^2+2\cdot x\cdot \frac{1}{x} +(\frac{1}{x})^2-2\cdot x\cdot \frac{1}{x} =(x+\frac{1}{x})^2-2\\\\x=2+ \sqrt{3} \ \ \ \Rightarrow\ \ \ x+ \frac{1}{x} =2+ \sqrt{3}+ \frac{1}{2+ \sqrt{3}} =2+ \sqrt{3}+ \frac{2- \sqrt{3} }{(2+ \sqrt{3})(2- \sqrt{3})} =\\\\=2+ \sqrt{3} + \frac{2- \sqrt{3} }{4-3} =2+ \sqrt{3} +2- \sqrt{3} =4\\\\x+ \frac{1}{x} =4\ \ \ \Rightarrow\ \ \ (x+\frac{1}{x})^2-2=4^2-2=16-2=14[/tex]
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