There exists a set of points such that their rectangular coordinates and their polar coordinates are the same. This set of points lies on a function that can be written as . What is ?
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If we call the rectangular coordinates ( x , y ) and the polar coordinates ( r , θ ) , we get that x = r and y = θ . Then, let’s use some rectangular polar conversion formulas.
x = r cos ( θ ) x = x cos ( θ ) cos ( θ ) = 1 θ = 2 π × n
Now, remember that an equation in the form θ = c is a line that goes through the origin, and an equation in the form y = c is a line that has a slope of zero. Because both of these equations need to result in the same line in this case, the only line that works is y = θ = 0 , where the constant c = 0 .
Wait, but what’s that you say? I made a mistake? Where? Aha! You have good eyes. In our work above, we divided by the variable x . But what if x = 0 ? Well, then, let’s use our other conversion formula.
y = r sin ( θ ) y = x sin ( θ ) y = 0 × sin ( θ ) y = 0
Again, we get to the same result, so we don’t have to change anything. We know that the equation of the line is y = 0 , which can be written as y = 0 x 2 + 0 x + 0 . Thus, a = b = c = 0 , and therefore, a + b + c = 0 .