Hearted Youtube comments on Mathologer (@Mathologer) channel.

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  41. For the puzzle at 11:37, I was too tired yesterday to get it, but now that I had time today I gave it another shot. My square was defined as: ┌──┬──┐ I defined the layout of any pythag.. triple as:. │B1│B2│ X^2 + Y^2 = Z^2 . ├──┼──┤ . │B4│B3│ . └──┴──┘ . I started out pretty standard with the main three equations of: B1*B4 = X 2*B2*B3 = Y B1*B3 + B2*B4 = Z I also included these: B1 + B2 = B3 B2 + B3 = B4 To define the innercircle, I used r_i to denote its radius. The equation is then: r_i = B1*B2 I started by creating an equation to find r_i. To do this, I used the slope of the hypotenuse (Y/X) to solve for an angle, divide it by two, and convert it back to a slope. This gives a slope which bisects the angle XZ. The equation is: y=tan(1/2 * arctan(Y/X)) * (x+X) (my origin is placed at the corner XY so x+X places the lines origin at the corner XZ) Using trig identities, namley half angle identity and inverse trig identities, I could simplify the expression: tan(1/2 * arctan(Y/X)) => (sin(arctan(Y/X))) / (1 + cos(arctan(Y/X))) => (((Y/X)/sqrt[1 + (Y/X)^2]) / (1 + (1/sqrt[1 + (Y/X)^2])) => (Y/X) / (sqrt[1 + (Y/X)^2] + 1) => Y / (sqrt[X^2 + Y^2] + X) This means that the equation is: y = (Y / (sqrt[X^2 + Y^2] + X))(x+X) Which is our equation for the first bisector line. Since the angle XY is 90°, it has a bisector with a slope of -1. This results in the equations: y=-x Setting them equal to find the centre of the incircle results in a simplified equation of: x = -XY / (X + Y + sqrt[X^2 + Y^2])) Since X^2 + Y^2 = Z^2, this becomes: x = -XY / (X + Y + Z)) OR: r_i = (XY) / (X+Y+Z) Plugging in the values, we get: r_i = 36 since r_i = B1*B2 = 36, this means B1 = 36/B2. plugging into the equation: B1 + B2 = B3 yields: 36/B2 + B2 = B3 => 36 = B2*B3 - B2^2 using Y = 2*B2*B3 = 104, we know B2*B3 = 52. 36 = 52 - B2^2 => B2^2 = 52-36 => B2 = 4. So, using B2*B3 = 52 we find: B3 = 13 Since B1 + B2 = B3: B1 + 4 = 13 Or: B1 = 9 Since B2 + B3 = B4: 4 + 13 = B4 Or: B4 = 17 To Conclude, my guess as to the numbers in the square are: ┌──┬──┐ │ 9│ 4│ ├──┼──┤ │17│13│ └──┴──┘
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