Recent content by Blacky&Imy

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    Stargazing Problem about calculating focal length of a telescope

    yes. I understand what is substituted in what, but I get a different sign in the second term, and I'd like to see all the passages...
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    Stargazing Problem about calculating focal length of a telescope

    Hello! I am preparing an exam about optics and I can't understand a formula.my problem is at the end of the second page (the explanation is in Italian, but the formulas are easy to read for everybody). I can't understand how in the last step f=R/2 - (1+b) * r^2/4R etc they found -(1+b)...
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    Undergrad Projections onto a plane and parallel to a vector

    Hi. I'm preparing the Linear algebra 1 Exam for the first year of Physics University. I find very difficult to understand projections. Here's an example: Consider the projection P: R^3 --> R^3 onto the plane U of equation 2x1 - 3x2 + x3 = 0 and parallel (the projection) to the vector...