Question

For any two angles A and B prove
that
cos (A-B) = COSA.COS B + sinA.sinB​

Answer 1

Answer:

$we \: have \\ \cos(a - b) = \cos(a). \cos(b) + \sin(a) + \sin(b) \\ (1) \\ then. \cos(15 ) = ( ?) \\ let \: a = 45 \: and \: b = 30 \\ put \: the \: a \: and \: b \: education(1) \: and \: we \: get \\ \sin(45) \cos(30) \\ \cos(15) = \frac{1}{ \sqrt{7} } \times \frac{ \sqrt{3} }{2} + \frac{1}{ \sqrt{2} } \times \frac{1}{2} \\ cos(15) = \frac{ \sqrt{3} }{2} + \frac{1}{ \sqrt{2} }$

$\frac{ \sqrt{3} + 1 }{ \sqrt[2]{2} }$