Hey guys, I am quite new to this forum, and just encountered this seemingly simple problem but still was not successful in solving it.

If,

then prove that,

where x,y and z are real numbers.

I tried everything I could from basic identities to substituting x=a+y and x=b+z which one of my friend suggested but no luck yet.

The 'prove that' part seems obvious but I cannot make out how to write a proof.

I would appreciate if you guys can help me out with this.