Question

Докажите тождество:

sin(a-β)-cos a sin(-β)=sin a cos β

Вычислите:

соs18° cos63°+sin18° sin63°

Answer 1

Вычислите:

соs18° cos63°+sin18° sin63° =  cos63°соs18°+sin63° sin18° = cos (63°-18°)= cos 45° =√2/2

 

Answer 2

$sin(alpha -beta)-cosalpha sin(-beta)=(sinalpha cosbeta-cosalpha sinbeta)-\ -cosalpha (-sinbeta)=sinalpha cosbeta$

 

cos18cos63+sin18sin63=cos(18-63)=cos(-45)=cos(45)=$frac{1}{sqrt2}$