Proving that $L=\{ \langle M \rangle \colon L(M)=L(M)^R \}$ is undecidable [duplicate]

I'm trying to show that $L=\{ \langle M \rangle \colon L(M)=L(M)^R\}$ is undecidable, but I don't even know where to begin. Google wasn't much of a help, maybe because it's hard describing the language in words. Any hints?
• What do you define $L(M)^{R}$ to be? – Ryan Jul 11 '15 at 20:28
• Every string in $L(M)^R$ is a reverse of some string in $L(R)$ – Yotam Jul 12 '15 at 7:42