The problem is to solve the quadratic equation $ix^2 + 2(1+i)x + 1 = 0$ for $x$.

AlgebraQuadratic EquationsComplex NumbersComplex Roots
2025/8/9

1. Problem Description

The problem is to solve the quadratic equation ix2+2(1+i)x+1=0ix^2 + 2(1+i)x + 1 = 0 for xx.

2. Solution Steps

We can use the quadratic formula to solve for xx. The quadratic formula for ax2+bx+c=0ax^2 + bx + c = 0 is given by:
x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
In this case, a=ia = i, b=2(1+i)b = 2(1+i) and c=1c = 1.
Substituting these values into the quadratic formula:
x=2(1+i)±(2(1+i))24(i)(1)2ix = \frac{-2(1+i) \pm \sqrt{(2(1+i))^2 - 4(i)(1)}}{2i}
First, let's simplify the expression under the square root:
(2(1+i))24(i)(1)=4(1+i)24i=4(1+2i+i2)4i=4(1+2i1)4i=4(2i)4i=8i4i=4i(2(1+i))^2 - 4(i)(1) = 4(1+i)^2 - 4i = 4(1 + 2i + i^2) - 4i = 4(1 + 2i - 1) - 4i = 4(2i) - 4i = 8i - 4i = 4i
So,
x=2(1+i)±4i2ix = \frac{-2(1+i) \pm \sqrt{4i}}{2i}
We need to find the square root of 4i4i. Let 4i=a+bi\sqrt{4i} = a + bi. Then (a+bi)2=4i(a+bi)^2 = 4i, which means a2+2abib2=4ia^2 + 2abi - b^2 = 4i.
Equating the real and imaginary parts, we have:
a2b2=0a^2 - b^2 = 0 and 2ab=42ab = 4, which implies ab=2ab=2.
From the first equation, a2=b2a^2 = b^2, so a=ba = b or a=ba = -b. Since ab=2>0ab = 2 > 0, aa and bb must have the same sign, so we have a=ba = b.
Substituting a=ba = b into ab=2ab = 2, we get a2=2a^2 = 2, so a=2a = \sqrt{2} or a=2a = -\sqrt{2}.
Then b=2b = \sqrt{2} or b=2b = -\sqrt{2}.
Therefore, 4i=2+i2\sqrt{4i} = \sqrt{2} + i\sqrt{2} or 4i=2i2\sqrt{4i} = -\sqrt{2} - i\sqrt{2}. We can take 4i=2+i2=2(1+i)\sqrt{4i} = \sqrt{2} + i\sqrt{2} = \sqrt{2}(1+i).
Substituting this back into the equation for xx:
x=2(1+i)±2(1+i)2i=(1+i)(2±2)2ix = \frac{-2(1+i) \pm \sqrt{2}(1+i)}{2i} = \frac{(1+i)(-2 \pm \sqrt{2})}{2i}
x=(1+i)(2±2)2iii=(1+i)(2±2)(i)2=(1+i)(2i2i)2=2i2i222x = \frac{(1+i)(-2 \pm \sqrt{2})}{2i} \cdot \frac{-i}{-i} = \frac{(1+i)(-2 \pm \sqrt{2})(-i)}{2} = \frac{(1+i)(2i \mp \sqrt{2}i)}{2} = \frac{2i \mp \sqrt{2}i - 2 \mp \sqrt{2}}{2}
x=22+i(22)2=122+i(122)x = \frac{-2 \mp \sqrt{2} + i(2 \mp \sqrt{2})}{2} = -1 \mp \frac{\sqrt{2}}{2} + i (1 \mp \frac{\sqrt{2}}{2})
So the two possible values of xx are x=122+i(122)x = -1 - \frac{\sqrt{2}}{2} + i(1 - \frac{\sqrt{2}}{2}) and x=1+22+i(1+22)x = -1 + \frac{\sqrt{2}}{2} + i(1 + \frac{\sqrt{2}}{2}).
x=2(1+i)±4i2i=2(1+i)±2i2i=(1+i)±iix = \frac{-2(1+i) \pm \sqrt{4i}}{2i} = \frac{-2(1+i) \pm 2\sqrt{i}}{2i} = \frac{-(1+i) \pm \sqrt{i}}{i}
Let i=1+i2\sqrt{i} = \frac{1+i}{\sqrt{2}}, then
x=1i±1+i2i=(1i±1+i2)ii2=(1i±1+i2)(i)=i+i2i12=i1i12=112+i12=1±12+i(1±12)x = \frac{-1-i \pm \frac{1+i}{\sqrt{2}}}{i} = (-1-i \pm \frac{1+i}{\sqrt{2}}) \frac{-i}{-i^2} = (-1-i \pm \frac{1+i}{\sqrt{2}})(-i) = i + i^2 \mp \frac{i-1}{\sqrt{2}} = i - 1 \mp \frac{i-1}{\sqrt{2}} = -1 \mp \frac{-1}{\sqrt{2}} + i \mp \frac{1}{\sqrt{2}} = -1 \pm \frac{1}{\sqrt{2}} + i(1 \pm \frac{1}{\sqrt{2}})
x=1±22+i(1±22)x = -1 \pm \frac{\sqrt{2}}{2} + i(1 \pm \frac{\sqrt{2}}{2})

3. Final Answer

The solutions are x=1+22+i(1+22)x = -1 + \frac{\sqrt{2}}{2} + i(1 + \frac{\sqrt{2}}{2}) and x=122+i(122)x = -1 - \frac{\sqrt{2}}{2} + i(1 - \frac{\sqrt{2}}{2}).