To prove that the graphs of the given curves are tangent
to each other, we'll solve the equation:
x^2 = x + 1 -
1/x
We'll multiply the term from the left side and the
first 2 terms from the right side, by x;
x^3 = x^2 + x -
1
We'll move all terms to one
side:
x^3 - x^2 - x + 1 =
0
We'll factorize by x^2 the first 2
terms:
x^2*(x-1) - (x-1) =
0
We'll factorize again by
(x-1):
(x-1)*(x^2-1) = 0
We'll
write the difference of squares (x^2 - 1) =
(x-1)(x+1)
We'll re-write the
product:
(x-1)*(x-1)*(x+1) =
0
We'll put each factor as
zero:
x-1 = 0
We'll add 1 both
sides:
x = 1
x+1 =
0
We'll add -1 both sides:
x =
-1
Since y = x^2, we'll
have;
For x = 1 => y =
1
For x = -1 => y =
1
So, the curves are tangent. The point where the 2 curves
are tangent is (1 , 1).
Now, we'll write the equation of
the line that passes through a point and it has a slope
m.
The slope m = y'(1).
y =
x^2 => y' = 2x
y'(1) =
2*1
y'(1) = 2
y'(1) =
m
m = 2
The equation of the
line is:
y - 1 = y'(1)*
(x-1)
y - 1 = 2(x-1)
We'll
remove the
brackets:
y-1-2x+2=0
We'll
combine like terms and the equation of the line, tangent to the curves,
is:
y - 2x + 1 =
0
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