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Yes, I am familiar with the formula you mentioned.
The given expression: cos 40 degrees cos 50 degrees minus sin 40 degrees sin 50 degrees can be rewritten as: cos(40 degrees + 50 degrees), which follows the formula cos(A + B) = cosAcosB - sinAsinB.
Now, let's substitute the values into the formula:
cos(40 degrees + 50 degrees) = cos(90 degrees).
As we know, the cosine of 90 degrees is 0. Therefore, the exact value of cos 40 degrees cos 50 degrees minus sin 40 degrees sin 50 degrees is 0.