how does one go about solving something such as:
conjugate(z+2-3i) = z+5+10i
Conjugates of actual complex numbers are very simple, but the inclusion of z trips me up
Let z = x+iy
z+2-3i = x+2 + (y-3)i
So, its conjugate is x+2 - (y-3)i
and your equation becomes
x+2 - (y-3)i = x+5 + (y+10)i
since the real and imaginary parts must be equal, there is no solution, since for no x,y is x+2=x+5 and y-3=y+10
I suspect some kind of typo...
I assume we are solving for z.
when we multiply conjugates we are to get a real number
(z+2-3i)(z+5+10i)
= z^2 + 5z + 10iz + 2z + 10 + 20i - 3iz - 15i - 30i^2
= z^2 + 7z + 7iz + 40
let z = a+bi
z^2 + 7z + 7iz + 40
= (a^2 + 2bi + b^2 i^2) + 7(a + bi) + 7i(a+bi) + 40
= a^2 + 2bi - b^2 + 7a + 7bi + 7ai - 7b + 40
= (a^2 - b^2 + 7a - 7b + 40) + (6b+7a)i
for this to be real, 6b+7a = 0, 6b = -7a
b = -7a/6
then the real part
= a^2 - 49a^2/36 + 7a + 49a/6 + 40
= (36a^2 - 49a^2 + 252a + 294a + 1440)/36
= (-13a^2 + 546a + 1440)/36
but the right side was
a+bi + 5 + 10i
= (a+5) + (b+10)i
then: (-13a^2 + 546a + 1440)/36 = a+5
-13a^2 + 546a + 1440 = 36a + 180
-13a^2 + 510a + 1260 = 0
13a^2 - 510a - 1260 = 0
I get a = appr 41.563 or a = appr -2.332
then the corresponding
b= -48.49 and b = 2.72
z = 41.563 - 48.49i OR z = -2.332 + 2.72i
let's check the 2nd one:
first part = z +2-3i
= -2.332 + 2.72i + 2+3i
= -.332 + 5.72i
right side = z+5+10i
= -2.332 + 2.72i + 5 + 10i
= 2.668 - 12.72i
OH NO, I was expecting them to be conjugates.
Where did i go wrong ????
(I will copy/paste my reply and study it carefully. Hopefully I will get back to you if I find my error)
I started off the same way as Steve and then ...
....you never know with complex numbers,
as it stands, I noticed a real silly error on my part.
I dropped the 20i - 15i in the 3rd line.
No fun correcting and seeing where it leads me
To solve the equation "conjugate(z + 2 - 3i) = z + 5 + 10i," you need to use the definition of the complex conjugate. In general, the conjugate of a complex number is obtained by changing the sign of its imaginary part.
For a complex number z = a + bi, where "a" represents the real part and "b" represents the imaginary part, its conjugate is denoted as z* or z bar and is given by z* = a - bi.
In this equation, you have an expression inside the conjugate function, which includes the variable z. To simplify, let's use the definition of the conjugate on the expression z + 2 - 3i inside the conjugate function:
conjugate(z + 2 - 3i) = conjugate(z) + conjugate(2 - 3i)
Now, applying the definition of the conjugate to z and 2 - 3i, we have:
z + 2 - 3i = z* + 2 - 3i*,
where z* is the conjugate of z and i* is the conjugate of i.
Next, we need to simplify the equation by expanding the conjugates. The conjugate of i is -i, so we have:
z + 2 - 3i = z* + 2 + 3i.
Now, we can separate the real and imaginary parts of the complex numbers:
(Re[z] + 2) + (-3)Im[z] = Re[z*] + 2 + 3Im[z*].
By comparing the real and imaginary parts on each side of the equation, you can write two separate equations:
Re[z] + 2 = Re[z*] + 2,
-3Im[z] = 3Im[z*].
Finally, simplify the equations further:
Re[z] = Re[z*],
Im[z] = -Im[z*].
These equations show that the real parts of z and z* are equal, and the imaginary parts of z and z* are equal in magnitude but opposite in sign.
From these equations, you can conclude that z and z* are complex conjugates of each other.
Overall, to solve the equation "conjugate(z + 2 - 3i) = z + 5 + 10i," you find that the real parts of z and z* are equal, and the imaginary parts of z and z* are equal in magnitude but opposite in sign. Therefore, z and z* are complex conjugates, and the equation is satisfied when z = -2 - 10i.