Sinasinb=1/2[cos(a-b)-cos(a+b)]
cosacosb=1/2[cos(a-b)+cos(a+b)]
sinacosb=1/2[sib(a-b)+sin(a+b)]
9.67
a)1/2)cosπ/4-cos2π/3)=1/2(√2/2+1/2)=(√2+1)/4
в)1/2(sinπ/4+sinπ/3)=1/2(√2/2+√3/2)=(√2+√3)/4
д)1/2cosπ/7+1/2cosπ/4-1/2cosπ/7+1/2cos2π/3=1/2*√2/2+1/2*(-1/2)=(√2-1)/4
9.68
а)1/2cosa+1/2cos3a-1/2cosa-1/2cos7a=1/2(cos3a-cos7a)=1/2*2sin2asin5a=
sin2asin5a
в)1/2sin(-a)+1/2sim3a-1/2sin(-a)-1/2sin7a=1/2(sin3a-sin7a)=1/2*2sin(-2a)cos5a=sin2acos5a