MATH110 December 2012
• Q1 (a) • Q1 (b) • Q2 (a) • Q2 (b) • Q2 (c) • Q2 (d) • Q2 (e) • Q2 (f) • Q3 (a) • Q3 (b) • Q3 (c) • Q3 (d) • Q4 • Q5 • Q6 • Q7 (a) • Q7 (b) • Q8 • Q9 (a) • Q9 (b) • Q9 (c) • Q10 •
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?
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If you are stuck, check the hints below. Read the first one and consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it! If after a while you are still stuck, go for the next hint.
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[show]Hint 1
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In order for a function to be differentiable over the domain, it should be differentiable within each piece of the function as well as on the boundary. What are the conditions for a function to be differentiable at a point? How is differentiability related to continuity?
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[show]Hint 2
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In order for a function to be differentiable at a point, the derivative must be equal on both sides of the point. Also, differentiable functions are also continuous, meaning that the value of the function must also be equal on both sides of any point.
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Checking a solution serves two purposes: helping you if, after having used all the hints, 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.
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[show]Solution
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In order for to be differentiable, the derivative at any point must be equal from both the left and right. Since is clearly differentiable at all points in other than x = 1, our point of interest is .
The derivative of at x = 1 from the left will be
which when evaluated at x = 1 gives
The derivative of at x = 1 from the right will be
To be differentiable, these must be equal, so
This gives us the value for a. Now we also know that in order for the function to be differentiable, it must also be continuous. In particular, this means both the right and left hand limits at x = 1 must be equal. So we have:
So will be differentiable when a = 1 and b = -1/2
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