Robert Israel

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18 years, 213 days
University of British Columbia
Associate Professor Emeritus
North York, Ontario, Canada

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These are replies submitted by Robert Israel

What does it mean for a line to be tangent to a curve at a point?
What does it mean for a line to be tangent to a curve at a point?
You have one of the conditions. Now something about the derivative?
You have one of the conditions. Now something about the derivative?
Let's start with one of the points. What do you know about the equation of the tangent line to the curve at x = x1?
Let's start with one of the points. What do you know about the equation of the tangent line to the curve at x = x1?
OK, so if your curve is y = f(x) and the tangent line is y = a*x+b, what equations say that the line is tangent to the curve at x=x1 and at x=x2?
OK, so if your curve is y = f(x) and the tangent line is y = a*x+b, what equations say that the line is tangent to the curve at x=x1 and at x=x2?
Perhaps a picture would help: Is this the situation you're interested in?
Perhaps a picture would help: Is this the situation you're interested in?
It first evaluates t numerically using evalf, then checks if the result "contains I", i.e. has a nonzero imaginary part. I put "contains I" in quotes because a complex float actually doesn't literally contain I in its internal representation, but "has" treats this as a special case. There may be a risk in some cases that a root that is actually real may appear to have a small imaginary part due to roundoff error, but that doesn't happen in this case.
It first evaluates t numerically using evalf, then checks if the result "contains I", i.e. has a nonzero imaginary part. I put "contains I" in quotes because a complex float actually doesn't literally contain I in its internal representation, but "has" treats this as a special case. There may be a risk in some cases that a root that is actually real may appear to have a small imaginary part due to roundoff error, but that doesn't happen in this case.
Yes, I am in the Mathematics Department at University of British Columbia.
Yes, I am in the Mathematics Department at University of British Columbia.
It looks like the D operator is not working on p. Hmmm, I see that happens in Maple 9.5. Well, replace D(p)(x) by diff(p(x),x) and it should work.
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