We are asked to find the standard form of the product of two complex numbers: $\sqrt{2}[\cos(\pi/4)+i\sin(\pi/4)]$ and $\sqrt{2}[\cos(7\pi/4)+i\sin(7\pi/4)]$.

AlgebraComplex NumbersPolar FormEuler's FormulaTrigonometry
2025/3/27

1. Problem Description

We are asked to find the standard form of the product of two complex numbers: 2[cos(π/4)+isin(π/4)]\sqrt{2}[\cos(\pi/4)+i\sin(\pi/4)] and 2[cos(7π/4)+isin(7π/4)]\sqrt{2}[\cos(7\pi/4)+i\sin(7\pi/4)].

2. Solution Steps

First, let's write the two complex numbers as z1=2[cos(π/4)+isin(π/4)]z_1 = \sqrt{2}[\cos(\pi/4)+i\sin(\pi/4)] and z2=2[cos(7π/4)+isin(7π/4)]z_2 = \sqrt{2}[\cos(7\pi/4)+i\sin(7\pi/4)].
We can find the product of z1z_1 and z2z_2 by multiplying their magnitudes and adding their angles.
The magnitude of z1z_1 is 2\sqrt{2} and the magnitude of z2z_2 is 2\sqrt{2}. Therefore, the magnitude of the product is 22=2\sqrt{2} \cdot \sqrt{2} = 2.
The angle of z1z_1 is π/4\pi/4 and the angle of z2z_2 is 7π/47\pi/4. Therefore, the angle of the product is π/4+7π/4=8π/4=2π\pi/4 + 7\pi/4 = 8\pi/4 = 2\pi.
So, the product is 2[cos(2π)+isin(2π)]2[\cos(2\pi) + i\sin(2\pi)].
Since cos(2π)=1\cos(2\pi) = 1 and sin(2π)=0\sin(2\pi) = 0, the product is 2[1+i(0)]=2[1]=22[1 + i(0)] = 2[1] = 2.
Alternatively, we can use Euler's formula: eiθ=cos(θ)+isin(θ)e^{i\theta} = \cos(\theta) + i\sin(\theta).
Then z1=2eiπ/4z_1 = \sqrt{2} e^{i\pi/4} and z2=2ei7π/4z_2 = \sqrt{2} e^{i7\pi/4}.
The product z1z2=(2eiπ/4)(2ei7π/4)=2ei(π/4+7π/4)=2ei(8π/4)=2ei2π=2(cos(2π)+isin(2π))=2(1+i(0))=2z_1 z_2 = (\sqrt{2} e^{i\pi/4})(\sqrt{2} e^{i7\pi/4}) = 2 e^{i(\pi/4 + 7\pi/4)} = 2 e^{i(8\pi/4)} = 2 e^{i2\pi} = 2(\cos(2\pi) + i\sin(2\pi)) = 2(1 + i(0)) = 2.

3. Final Answer

The final answer is
2.

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