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Step * of Lemma rcos-rsub

∀[x,y:ℝ].  (rcos(x - y) = ((rcos(x) * rcos(y)) + (rsin(x) * rsin(y))))
BY
{ (Auto THEN (InstLemma `rcos-radd` [⌜x⌝;⌜-(y)⌝]⋅ THENA Auto)) }

1
1. x : ℝ
2. y : ℝ
3. rcos(x + -(y)) = ((rcos(x) * rcos(-(y))) - rsin(x) * rsin(-(y)))
⊢ rcos(x - y) = ((rcos(x) * rcos(y)) + (rsin(x) * rsin(y)))

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Latex:

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Latex:
\mforall{}[x,y:\mBbbR{}].    (rcos(x  -  y)  =  ((rcos(x)  *  rcos(y))  +  (rsin(x)  *  rsin(y))))


By

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Latex:
(Auto  THEN  (InstLemma  `rcos-radd`  [\mkleeneopen{}x\mkleeneclose{};\mkleeneopen{}-(y)\mkleeneclose{}]\mcdot{}  THENA  Auto))

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