Monday, August 11, 2014

Prove that the graph of the curve y=x^2 is tangent to the graph of the curve y=x+1-1/x.Write the equation of the tangent line in the intercepting...

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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