y = 2x+1/x+2
To find the
inverse function:
Solution:
y
= 2x+1/x+2. Multiply by
x.
yx=2x^2+1+2x.
2x^2+(2-y)y+2.
x1
= {(y-2))+sqrt[(y-2)^2-4]}/2*2
x1 = {(2-y) -
sqrt((y-4)y)}/4
x2 = {(2-y)
-sqrt(y(y-2)y}/4.
Therefore , there is no inverse funtion
as y has the same value for two different values of x = x1 and x2. Thus set of x and
the set of y f(x) is not a bijection.
Also y' =
(2x^2+1/x+2)' = 0 gives 2-1/x^2=0 giving x1 = 1/sqrt2 and x2 =
-1/sqrt
y"(x1) = -1/x1^2 = -1/sqrt2
<0
y"(x2) = - (-1/sqrt2)= 1sqrt. >
0
So y has minimum 2(1/sqrt1)+1/(1/sqrt2) +2 = 2(1+sqrt2)
at x = 1/sqrt2.
Y has a maximum of
2/(-sqrt2)+1/(-1/sqrt2)+2 = 2(1-sqrt2) at x= -1/sqrt2.
At x
= 0 , y is not defined,
At x = 0, y(x+1/x) has avertical
asynptote,
As Lt x--> 0+ tha y value is
inf.
As Lt x--> 0- the y value is -
inf.
2x+2 is the straight line which is an oblique
asymptote( as x --> infinity or x -->
infinity).
So there are four domains where the function is
bijective.
(i) When x >=1/sqrt2, y= 2x+1/x+2 is
bijective with inverse function:
x = {(y-2)+sqrt[(y-2)^2
-8]}/2*2
(ii) when 0 < x < =
1/sqrt2
x = {(y-2)+sqrt[(y-2)^2-8] }
/4
(iii) when -1/sqrtx < = x <
0.
x = {(y-2) -
sqrt[(y-2)^2-8]}/4
(iV) When x < =
-1/sqrt2.
x= {(y-2) - sqrt{y-2)^2
-8}/4.
y has no value in the open interval ] 2(1-sqrt2 ,
2(1+sqrt2) [ .
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