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Thread: Yes, this is a homework question...

  1. #1 Yes, this is a homework question... 
    Forum Freshman Keith's Avatar
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    ...which I know you guys don't like, but I'm really stuck. Just starting calculus wee....

    Find the values of the constants a and b, that makes the differentiable at the point where the rule for the function changes.

    Code:
    f(x)={ax^2+10, x<2
          x^2-bx, x≥2
    yea so thats like a split function.

    TIA


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  3. #2  
    Forum Professor river_rat's Avatar
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    Hey Keith

    You need to remember two things here

    1. If a function has a derivative at a point then it is continuous at that point. So look at the limits of f(x) as x->2 from the right and left and equate them.

    2. The derivative is a limit, so it exists if its left and right limits exist. This boils down to taking the derivative of each piece seperately and equating them when x=2.

    So solve these two equations and you should get your result.


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  4. #3  
    Forum Freshman Keith's Avatar
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    I was doing that (still am) but every time I end up with the same wrong values for a and b. I get b=-10 and a=3.5. I guess I'll get it eventually.

    Thanks.

    EDIT:Well, it seems that is what everyone else got. It doesn't seem to check though.

    EDIT2:NVM I got it!
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