oh sorri i mean in(x+y+z)=sinXcosYcosZ+cosXsinYcosZ+cosXcosYsinZ-sinXsinYsinZ

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<p>this is the sum formula right?
but whats getting me confused is this has an extra variable
how am i suppose to prove it ?
sin(x+y+z)=sinXcosYcosZ+cosXsinYcosZ+cosXcosYsinZ-sinXsinYsinZ</p>