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Let Phi: R rightarrow S be a homomorphism from the ring R to the ring S and let K = {r R such that Phi(r) = 0S}. Prove that K is a subring of R.

Show transcribed image text Let Phi: R rightarrow S be a homomorphism from the ring R to the ring S and let K = {r R such that Phi(r) = 0S}. Prove that K is a subring of R.