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

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) (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.
------
f(x) = x^4-16
------
f(1-sqrt(5)) = (1-sqrt(5))^4 - 16
Note: That is a difference of squares.
Factor::
------
= [(1-sqrt(5))^2-4)]
------
Square the squaring terms::
= [1+5-2sqrt(5)-4]
-------
= [2-2sqrt(5)]
-------
= [2(1-sqrt(5))]
--------
= 4(1-sqrt(5))(5-sqrt(5))
--------
= [4(5-6sqrt(5))+5]
--------
= 20-24sqrt(5) + 5
----------------
= 25 - 24sqrt(5)
====================
Cheers,
Stan H.
====================
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