Cos 50° cos 31° – sin 50° sin 31° =

http://www.sosmath.com/trig/prodform/pro… -- Has the product to sum identities, which were used here

cos 50 * cos 31 = 1/2 * (cos 81 + cos 19)
sin 50 * sin 31 = 1/2 * ( cos 19 - cos 81)

Subtracting these two:
1/2 (cos 81 + cos 19) - 1/2 (cos 19 - cos 81)

Factor out a 1/2:
1/2 ( cos 81 + cos 19 - cos 19 + cos 81)

cos 19 cancels out, so the answer is
(2 cos 81)/2 = cos 81

cos 50° cos 31° – sin 50° sin 31°
there's no big calculation to do here there's just one formula u should remember

cos(x+y) = cosXcosY - sinXsinY

therefore
cos 50° cos 31° – sin 50° sin 31° = cos(50 +31) = cos 81°= 0.156

It looks like this is of the form

cosAcosB - sinAsinB

In that case, the answer would be cos(A+B) which is cos 81. So that's 0.15643

Hope I could help you out! :)

Use ur calculator u will get 0.1564