I don't know if this is how you've seen it, but the version of de Moivre's theorem in my textbook is r^(1/n)*(cos((x + 2pi*k)/n) + i*sin((x + 2pi*k)/n)). I can't seem to find any videos on de Moivre's theorem, either, but I do know that the idea that (cos x + i*sin x)^n = cos(nx) + i*sin(nx) can be derived from Euler's formula. The red line is the parabola that you normally get when using only real coordinates Plot3(realPart, zeros(1,numberOfPointsOnTheAxis). ImaginaryPart(:) * ones(1,numberOfPointsOnTheAxis) * 1i X = ones(numberOfPointsOnTheAxis,1) * realPart(:)' +. ImaginaryPart = linspace(-2,2,numberOfPointsOnTheAxis) RealPart = linspace(1,4,numberOfPointsOnTheAxis) P = % 1*x*x -6*x +10 the coefficients of the polynomial I came up with the following piece of code written in MATLAB: You could make two representations, one for the real value of the result and one for the imaginary value of the result, but you would have to search for the point(s) where those 2 are both 0. The absolute value is always non-negative, and the solutions to the polynomial are located at the points where the absolute value of the result is 0. You would put the absolute value of the result on the z-axis when x is real (complex part is 0) the absolute value is equal to the value of the polynomial at that point. Now we use our algebra skills to solve for "x".I think a way to do that is to make a 3D chart that has the complex coordinates on the horizontal axis. Total time = time upstream + time downstream = 3 hours (to travel 8 km at 4 km/h takes 8/4 = 2 hours, right?) We can turn those speeds into times using: when going downstream, v = x+2 (its speed is increased by 2 km/h).when going upstream, v = x−2 (its speed is reduced by 2 km/h).Let v = the speed relative to the land (km/h)īecause the river flows downstream at 2 km/h:.Let x = the boat's speed in the water (km/h).There are two speeds to think about: the speed the boat makes in the water, and the speed relative to the land: What is the boat's speed and how long was the upstream journey? The negative value of x make no sense, so the answer is:Įxample: River Cruise A 3 hour river cruise goes 15 km upstream and then back again. The desired area of 28 is shown as a horizontal line. There are many ways to solve it, here we will factor it using the "Find two numbers that multiply to give ac, and add to give b" method in Factoring Quadratics: It looks even better when we multiply all terms by −1: (Note for the enthusiastic: the -5t 2 is simplified from -(½)at 2 with a=9.8 m/s 2)Īdd them up and the height h at any time t is:Īnd the ball will hit the ground when the height is zero: Gravity pulls it down, changing its position by about 5 m per second squared: It travels upwards at 14 meters per second (14 m/s): (Note: t is time in seconds) The height starts at 3 m: Ignoring air resistance, we can work out its height by adding up these three things:
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