# Khan/khan-exercises

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 Multiplying and dividing complex number polar forms

Multiply the following complex numbers, marked as blue dots on the graph:

LEFT_BRACKETA_REPRIGHT_BRACKET \cdot LEFT_BRACKETB_REPRIGHT_BRACKET

graphInit({ range: [ [ -10, 10 ], [ -10 ,10 ] ], scale: 20, tickStep: 1, axisArrows: "<->" }); drawComplexChart( 10, DENOMINATOR ); circle( [A_REAL, A_IMAG], 1 / 4, { fill: KhanUtil.BLUE, stroke: "none" }); circle( [B_REAL, B_IMAG], 1 / 4, { fill: KhanUtil.BLUE, stroke: "none" }); graph.currComplexPolar = new ComplexPolarForm( DENOMINATOR, 10, USE_EULER_FORM ); redrawComplexPolarForm();
Angle: 0
1
redrawComplexPolarForm(guess[0], guess[1]);
redrawComplexPolarForm(guess[0], guess[1]);

Multiplying complex numbers in polar forms can be done by multiplying the lengths and adding the angles.

The sum of the angles is A_ANGLE_REP + B_ANGLE_REP = INTERMEDIATE_ANGLE_REP.

The angle INTERMEDIATE_ANGLE_REP is more than 2 \pi. A complex number goes a full circle if its angle is increased by 2 \pi, so it goes back to itself. Because of that, angles of complex numbers are convient to keep between 0 and 2 \pi.

INTERMEDIATE_ANGLE_REP - 2 \pi = ANSWER_ANGLE_REP

The angle of the result is A_ANGLE_REP + B_ANGLE_REP = ANSWER_ANGLE_REP.

Divide the following complex numbers:

\dfrac{A_REP}{B_REP}

(The dividend is plotted in blue and the divisor in plotted in green. Your current answer will be plotted orange.)

graphInit({ range: [ [ -10, 10 ], [ -10, 10 ] ], scale: 20, tickStep: 1, axisArrows: "<->" }); drawComplexChart( 10, DENOMINATOR ); circle( [A_REAL, A_IMAG], 1 / 4, { fill: KhanUtil.BLUE, stroke: "none" }); circle( [B_REAL, B_IMAG], 1 / 4, { fill: KhanUtil.GREEN, stroke: "none" }); graph.currComplexPolar = new ComplexPolarForm( DENOMINATOR, 10, USE_EULER_FORM ); redrawComplexPolarForm();
Angle: 0
1
redrawComplexPolarForm(guess[0], guess[1]);
redrawComplexPolarForm(guess[0], guess[1]);

Dividing complex numbers in polar forms can be done by dividing the radii and subtracting the angles.