SOLUTION: my problem is x^4-16 it says to plug in 1- the square root of 5 in my x spot. I do that and get a number and they say it is wrong, they want an expression like 15- 3 the square ro

Algebra ->  Exponents -> SOLUTION: my problem is x^4-16 it says to plug in 1- the square root of 5 in my x spot. I do that and get a number and they say it is wrong, they want an expression like 15- 3 the square ro      Log On


   

Question 803858: my problem is x^4-16 it says to plug in 1- the square root of 5 in my x spot.
I do that and get a number and they say it is wrong, they want an expression like 15- 3 the square root of 5. But i cant figure out how to get an answer like that
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
x^4-16 it says to plug in 1- the square root of 5 in my x spot.
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f(x) = x^4-16
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f(1-sqrt(5)) = (1-sqrt(5))^4 - 16
Note: That is a difference of squares.
Factor::
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= [(1-sqrt(5))^2-4)]
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Square the squaring terms::
= [1+5-2sqrt(5)-4]
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= [2-2sqrt(5)]
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= [2(1-sqrt(5))]
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= 4(1-sqrt(5))(5-sqrt(5))
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= [4(5-6sqrt(5))+5]
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= 20-24sqrt(5) + 5
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= 25 - 24sqrt(5)
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Cheers,
Stan H.
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