How do you find the area bounded by #y=(x+1)/x#, #y=x^2+1# and x=2?

1 Answer
Feb 9, 2017

The area is #7/3 - ln2 ~~1.64# square units.

Explanation:

Start by finding the intersection points.

#x^2 + 1 = (x + 1)/x#

#x^3 + x = x + 1#

#x^3 = 1#

#x = 1#

This means that #y= 1^2 + 1 = 2#.

Now complete a rudimentary sketch of the graphs.

enter image source here

So we have bounds of integration of #[1, 2]# (this is why we found the intersection points), and we know the parabola lies above the rational function. The integral to evaluate will therefore be:

#int_1^2 x^2 + 1 - (x+ 1)/x dx#

#=int_1^2 (x^3 + x - x - 1)/xdx#

#=int_1^2 (x^3 - 1)/x dx#

#=int_1^2 x^2 - 1/xdx#

#=[1/3x^3 - ln|x|]_1^2#

Evaluate using #int_a^bF(x) = f(b) - f(a)#, where function #f(x)# is continuous on #[a, b]# and #f'(x) = F(x)#.

#=1/3(2)^3 - ln|2| - (1/3(1)^3 - ln|1|)#

#= 8/3 - ln2 - 1/3 + 0#

#= 7/3 - ln2#

Hopefully this helps!