Science:Math Exam Resources/Courses/MATH101/April 2005/Question 02 (a)

MATH101 April 2005

  •  Q1 (a)  •  Q1 (b)  •  Q1 (c)  •  Q1 (d)  •  Q1 (e)  •  Q1 (f)  •  Q1 (g)  •  Q2 (a)  •  Q2 (b)  •  Q2 (c)  •  Q2 (d)  •  Q3 (a)  •  Q3 (b)  •  Q3 (c)  •  Q4  •  Q5 (a)  •  Q5 (b)  •  Q6 (a)  •  Q6 (b)  •  Q7 (a)  •  Q7 (b)  •  Q7 (c)  •  Q8 (a)  •  Q8 (b)  •  

   Other MATH101 Exams

  •  April 2011  •  April 2010  •  April 2009  •  April 2008  •  April 2007  •  April 2005  •  April 2006  •  April 2012  •  April 2013  •  April 2014  •  April 2015  •  April 2016  •  April 2018  •  April 2017  •  

Question 02 (a)
Full-Solution Problem. Justify your answer and show all your work. Simplification of your answer is not required. Let $\displaystyle R$ be the finite region bounded above by the curve $\displaystyle y=4-x^{2}$ and bounded below by $\displaystyle y=2-x$. Carefully sketch $\displaystyle R$ and find its area explicitly.

Make sure you understand the problem fully: What is the question asking you to do? Are there specific conditions or constraints that you should take note of? How will you know if your answer is correct from your work only? Can you rephrase the question in your own words in a way that makes sense to you?

If you are stuck, check the hint below. Consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it!

Hint
There are two key things to figure out. One is the points of intersection and the other is which curve is larger on the region of integration.

Checking a solution serves two purposes: helping you if, after having used the hint, you still are stuck on the problem; or if you have solved the problem and would like to check your work. If you are stuck on a problem: Read the solution slowly and as soon as you feel you could finish the problem on your own, hide it and work on the problem. Come back later to the solution if you are stuck or if you want to check your work. If you want to check your work: Don't only focus on the answer, problems are mostly marked for the work you do, make sure you understand all the steps that were required to complete the problem and see if you made mistakes or forgot some aspects. Your goal is to check that your mental process was correct, not only the result.

Solution

A picture can be found below. First, we find the points of intersection. Set the curves equal to each other so that $\displaystyle 4-x^{2}=2-x$ Then isolating to one side gives $\displaystyle 0=x^{2}-x-2=(x+1)(x-2)$ and so the x coordinates of the points of intersection are $x=-1,2$. Now, plugging in the point $x=0$ into both curves shows that $4-x^{2}$ is the upper most curve. Hence, the area we seek is ${\begin{aligned}A&=\int _{-1}^{2}(4-x^{2}-(2-x))\,dx\\&=\int _{-1}^{2}(-x^{2}+x+2)\,dx\\&=\left.\left({\frac {-x^{3}}{3}}+{\frac {x^{2}}{2}}+2x\right)\right|_{-1}^{2}\\&=\left({\frac {-8}{3}}+{\frac {4}{2}}+2(2)\right)-\left({\frac {1}{3}}+{\frac {1}{2}}+2(-1)\right)\\&={\frac {-8}{3}}+6-{\frac {1}{3}}-{\frac {1}{2}}+2\\&=-3+{\frac {15}{2}}\\&={\frac {9}{2}}\end{aligned}}$ completing the question.

Click here for similar questions

MER QGH flag, MER QGQ flag, MER QGS flag, MER RT flag, MER Tag Area between two curves, Pages using DynamicPageList3 parser function, Pages using DynamicPageList3 parser tag