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Homework Help: 2 Calculus questions

  1. Dec 14, 2004 #1
    I have two Calculus problems I need explained because I'm studying for a final exam and I forgot how to do these things:

    #1: Find the point that lies on the line determined by the points (1,-2) and (-3,1).

    The answer is (5,-5), but I don't know why....

    #2: Write an equation satisfied by the graph obtained by shifting y=2x-5 three units to the left.

    The answer is y=2x+1

    I know when an equation is shown moving to the left, it is put in parentheses and a number is added to it (for example y=x^2 becomes y=(x^2+2) when it is moved two places to the left). However, I do not know how to do this problem.

    Could someone please help me?
  2. jcsd
  3. Dec 14, 2004 #2
    Several things you can do. First off, these aren't calc questions, afaik.

    1. Can you write down the equation determined by the two points? If so, then I guess you have choices to plug into the equation to see if they work.

    2. The easiest thing to do is to just plot the thing and move it 3 units to the left, and see what you get. But you can also just apply some transforms. In your case, you can shift your function to the left ( f(x) -> f(x+3) ) by applying that transform.

    See what you get :)
  4. Dec 14, 2004 #3
    Thanks for the reply! I think I'm starting to remember this...

    Yeah I know these aren't really calc questions, but they were in the begining section of my calc. book.

    Thanks for your help!
  5. Dec 14, 2004 #4
    Anytime :D
  6. Dec 14, 2004 #5
    Okay, I'm still having trouble with the second question. I know I may sound really stupid, but I tried to solve it by doing f(x)=(2x-5+3), and did not get the correct answer. What am I doing incorrectly?
  7. Dec 14, 2004 #6
    Consider rewriting f(x) = 2x-5 as f(x) = 2(x-5/2).. and see if you get anything from there...
  8. Dec 14, 2004 #7
    Now I understand! I was having a bit of a mental block at hte moment... Thank you very much! :)
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