If (x-1/x)=5 then find the value of x^4+1/x^4
Answers
Answer:
Step-by-step explanation:
If x + 1/x =5 then find the value of x^4 +1/x^4?
x+1x=5
then
(x+1x)2=25
or
x2+2+1x2=25
or
x2+1x2=23
therefore
(x2+1x2)2=232
or
x4+2+1x4=529
or
x4+1x4=527.
Let’s try the direct method.
x+1x=5
therefore
x2–5x+1=0.
(One should say that x≠0, but x=0 does not satisfy the equation.)
The (two) possible values for x are
x=12(5±21−−√).
Let’s calculate x4 and 1/x4.
First notice that the product of both roots are 1, then one is the reciprocal of the other, and the roles of x4 and 1/x4 are interchanged.
(5+21−−√2)(5−21−−√2)
=25–214=1.
(We could had seen that from the independent term in the equation above, which is the product of the roots).
Now let’s calculate the fourth power of the roots.
First the square
(5±21−−√2)2
=25±1021−−√+214
=23±521−−√2.
Now the fourth power
(5±21−−√2)4
=(23±521−−√2)2
=232±23021−−√+25⋅214
=527±11521−−√2.
Last step, add the fourth power of the roots together
527+11521−−√2+527−11521−−√2=527.
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