We are given the complex numbers $z_1 = -1 + i\sqrt{3}$ and $z_2 = 1 - i\sqrt{3}$. We need to compute $z_1 + z_2$, $z_1 - z_2$, and $z_1 \times z_2$. Then we need to write the complex numbers $z_1 - z_2$ and $z_1 \times z_2$ in trigonometric form.

AlgebraComplex NumbersComplex Number ArithmeticTrigonometric FormModulusArgument
2025/5/11

1. Problem Description

We are given the complex numbers z1=1+i3z_1 = -1 + i\sqrt{3} and z2=1i3z_2 = 1 - i\sqrt{3}. We need to compute z1+z2z_1 + z_2, z1z2z_1 - z_2, and z1×z2z_1 \times z_2. Then we need to write the complex numbers z1z2z_1 - z_2 and z1×z2z_1 \times z_2 in trigonometric form.

2. Solution Steps

First, let's compute z1+z2z_1 + z_2:
z1+z2=(1+i3)+(1i3)=1+1+i3i3=0z_1 + z_2 = (-1 + i\sqrt{3}) + (1 - i\sqrt{3}) = -1 + 1 + i\sqrt{3} - i\sqrt{3} = 0
Next, let's compute z1z2z_1 - z_2:
z1z2=(1+i3)(1i3)=11+i3+i3=2+2i3z_1 - z_2 = (-1 + i\sqrt{3}) - (1 - i\sqrt{3}) = -1 - 1 + i\sqrt{3} + i\sqrt{3} = -2 + 2i\sqrt{3}
Now, let's compute z1×z2z_1 \times z_2:
z1×z2=(1+i3)(1i3)=1+i3+i3i2(3)=1+2i3+3=2+2i3z_1 \times z_2 = (-1 + i\sqrt{3})(1 - i\sqrt{3}) = -1 + i\sqrt{3} + i\sqrt{3} - i^2(3) = -1 + 2i\sqrt{3} + 3 = 2 + 2i\sqrt{3}
Now we need to write z1z2z_1 - z_2 and z1×z2z_1 \times z_2 in trigonometric form.
For z1z2=2+2i3z_1 - z_2 = -2 + 2i\sqrt{3}, the modulus is
r=(2)2+(23)2=4+12=16=4r = \sqrt{(-2)^2 + (2\sqrt{3})^2} = \sqrt{4 + 12} = \sqrt{16} = 4.
The argument θ\theta satisfies tan(θ)=232=3\tan(\theta) = \frac{2\sqrt{3}}{-2} = -\sqrt{3}. Since the complex number is in the second quadrant, θ=2π3\theta = \frac{2\pi}{3}.
So z1z2=4(cos(2π3)+isin(2π3))z_1 - z_2 = 4(\cos(\frac{2\pi}{3}) + i\sin(\frac{2\pi}{3})).
For z1×z2=2+2i3z_1 \times z_2 = 2 + 2i\sqrt{3}, the modulus is
r=22+(23)2=4+12=16=4r = \sqrt{2^2 + (2\sqrt{3})^2} = \sqrt{4 + 12} = \sqrt{16} = 4.
The argument θ\theta satisfies tan(θ)=232=3\tan(\theta) = \frac{2\sqrt{3}}{2} = \sqrt{3}. Since the complex number is in the first quadrant, θ=π3\theta = \frac{\pi}{3}.
So z1×z2=4(cos(π3)+isin(π3))z_1 \times z_2 = 4(\cos(\frac{\pi}{3}) + i\sin(\frac{\pi}{3})).

3. Final Answer

z1+z2=0z_1 + z_2 = 0
z1z2=2+2i3=4(cos(2π3)+isin(2π3))z_1 - z_2 = -2 + 2i\sqrt{3} = 4(\cos(\frac{2\pi}{3}) + i\sin(\frac{2\pi}{3}))
z1×z2=2+2i3=4(cos(π3)+isin(π3))z_1 \times z_2 = 2 + 2i\sqrt{3} = 4(\cos(\frac{\pi}{3}) + i\sin(\frac{\pi}{3}))

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