Carelessness in maths

• eagle

  4 Nov 11, 08:51

  Originally posted by wee_ws:

  Hi,

    Thanks eagle for your encouragement :)

    I made this mistake in this question about transformation on one occasion. Given the graph of y = f(2x), one is asked to sketch the graph of y = f(2x - 4). I simply took it as a translation of 4 units to the right when it should have been a translation of 2 units to the right.

    Thus one should ask what substitution should x be made to decide on the correction transformation. In the example, x is substituted with x - 2 to obtain f(2x - 4) from f(2x).

    Thanks.

  Cheers,
  Wen Shih

  That's right.

  I have a method which reduces the careless mistakes and improves understanding on these type of questions. It also helps students to easily understand how to transform from f(x) t0 f(-|x|).

  This method is also applicable to transformations in conics, and good to link between conics transformation and normal curves transformation.

  Will find some time to put my ideas into words on paper and pass it to you.

   

  Thanks ;)

• wee_ws

  4 Nov 11, 12:46

  Dear eagle,

    Thanks in advance!

  Cheers,
  Wen Shih

• wee_ws

  6 Nov 11, 12:30

  Hi,

    Here is another example of a mistake.

    A student wishes to find least n from the following inequality:

    P(-sqrt(n)/2 < Z < sqrt(n)/2) > 0.95.

    She uses GC to find the inverse Normal of 0.95.

    Thanks.

  Cheers,
  Wen Shih