Question

вычислить cos3a+2cos(п-3а)sin в квадр.(п/4-1,5а) при а=5п/36

Answer 1

cos3a-2cos3a*1/2(1-cos(π/2-3a)=cos3a-cos3a*(1-sin3a)=cos3a-cos3a+cos3asin3a= cos3asin3a=1/2sin6a=1/2sin(6*5π/36)=1/2sin5π/6=1/2sin(π-π/6)=1/2*sinπ/6=1/2*1/2=1/4