sorry for all these questions but ive recently started IB maths higher without doing Add maths for GCSE so im in need of a bit of help.

ok ive got this question:

-2+bi is a solution to z^2+az+(3+a)=0 find a and b given that they are real.

so i already know that -2-bi is another solution.... NOW WHAT!?!

"Like a midget at a urinal, I was going to have to stay on my toes"

"Like a blind man at an orgy, I was going to have to feel my way through"

substitute z = -2 +bi into the equation z^2 +az + (3+a) = 0. Then substitute z = -2 - bi. Then you have two equations, and two unknowns (a, and b). Expand and solve.
you make something like this (-2+bi)(-2-bi) and you put them together through multiplication and distribution
Quote by horny_cactus
Who's Rick Roll? Sorry for my ignorance I just joined this forum so I don't yet Know that member.
i honestly dont know thats just what i would do
sorry for double post
Quote by horny_cactus
Who's Rick Roll? Sorry for my ignorance I just joined this forum so I don't yet Know that member.
i is the square root of negative 1

and i think the first guy got it...im doing it atm.
"Like a midget at a urinal, I was going to have to stay on my toes"

"Like a blind man at an orgy, I was going to have to feel my way through"

Meh math noob time...

Is it a quadratic, having a a and c... You could use the discriminant and then factorise...Or just bash it with the full quadratic formula...Idk.
Ok. So you got the other solution. Now you see that real part of both solutions is -2. Let's say that formula is (-y +- sqrt(y^2 - 4xz)/2x
x = 1
y = a
z = 3+a

Well, real part of both solutions is -2. it is equal to -y / 2x. So y = 4 x.

x = 1 therefore y = 4.

y = a so a = 4 too.

z = 3+a = 3+4=7

edit: I fotgot b XD

bi = sqrt (y^- 4 xz) / 2x

bi = sqrt (-3)

b = sqrt (3)

Just ask if you don't understand my way of solving...
Last edited by -Rodion- at Nov 13, 2008,
yeah, I get a = 4, and b = sqrt(3)
I reeeaaally should start paying attention on math lessons :S
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meh imaginary numbers are so pointless
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bi - 2 = lonely man
how did u get b= sqrt3
i got (sqrt5)/2
"Like a midget at a urinal, I was going to have to stay on my toes"

"Like a blind man at an orgy, I was going to have to feel my way through"

+- bi = +- sqrt (y^2 - 4xz) / 2x

y^2 - 4xz = 16 - 4*7 = -12

+- bi = sqrt (-12) / 2 = sqrt ( -12/4) = sqrt (-3)
So when does this kind of stuff fit into your daily life ?