Gaussian integers, ring homomorphism and kernel

[rayman123]

Homework Statement

let [tex]\varphi:\mathbb{Z}\rightarrow \mathbb{Z}_{2}[/tex] be the map for which $$\varphi(a+bi)=[a+b]_{2}$$
a)verify that $$\varphi$$ is a ring homomorphism and determine its kernel
b) find a Gaussian integer z=a+bi s.t $$ker\varphi=(a+bi)$$
c)show that $$ker\varphi$$ is maximal ideal in [tex]\mathbb{Z}[/tex]

I started by showing that $$\varphi$$ preserves the ring operations
$$\varphi((a+bi)+(c+di))=\varphi((a+c)+(b+d)i)=[(a+c)+(b+d)]_{2}=[a+b]_{2}\oplus[c+d]_{2}=\varphi(a+bi)+\varphi(c+d)$$
and multiplication
$$\varphi((a+bi)(c+di))=\varphi(ac+adi+bic-bd)=\varphi((ac-bd)+(ad+bc)i)=[(ac-bd)+(ad+bc)]_{2}=ac-bd+ad+bc$$
but something is not right here because if I look at the right hand side, I should get
$$\varphi(a+bi)\varphi(c+di)=[a+b]_{2}[c+d]_{2}=[(a+b)(c+d)]_{2}=ac+ad+bc+bd$$...

I don't know how to find the kernel, I know that by def [tex]ker\varphi=\{z\in\mathbb{Z}; \varphi(z)=[0]_{2}\}[/tex]
please help :D

 

[micromass]

Homework Statement

let [tex]\varphi:\mathbb{Z}\rightarrow \mathbb{Z}_{2}[/tex] be the map for which $$\varphi(a+bi)=[a+b]_{2}$$
a)verify that $$\varphi$$ is a ring homomorphism and determine its kernel
b) find a Gaussian integer z=a+bi s.t $$ker\varphi=(a+bi)$$
c)show that $$ker\varphi$$ is maximal ideal in [tex]\mathbb{Z}[/tex]

I started by showing that $$\varphi$$ preserves the ring operations
$$\varphi((a+bi)+(c+di))=\varphi((a+c)+(b+d)i)=[(a+c)+(b+d)]_{2}=[a+b]_{2}\oplus[c+d]_{2}=\varphi(a+bi)+\varphi(c+d)$$
and multiplication
$$\varphi((a+bi)(c+di))=\varphi(ac+adi+bic-bd)=\varphi((ac-bd)+(ad+bc)i)=[(ac-bd)+(ad+bc)]_{2}=ac-bd+ad+bc$$
but something is not right here because if I look at the right hand side, I should get
$$\varphi(a+bi)\varphi(c+di)=[a+b]_{2}[c+d]_{2}=[(a+b)(c+d)]_{2}=ac+ad+bc+bd$$...

Maybe bd=-bd (mod 2) ??

I don't know how to find the kernel, I know that by def [tex]ker\varphi=\{z\in\mathbb{Z}; \varphi(z)=[0]_{2}\}[/tex]
please help :D

Yes, so take $a+bi \in \ker(\varphi$. Then $\varphi(a+bi)=0$. Now just write things out using the definition of $\varphi$.