помоогиитее пожалуйстаа!!!!!!

  • 1a)1/2(sin30+sin40)=1/2*1/2+1/2sin40=1/4+1/2sin40
    b)1/2cos60+1/2cos14=1/2*1/2+1/2cos14=1/4+1/2cos14
    c)1/cos12-1/2cos60=1/2cos12-1/4
    2a)sin(90-20)cos(90-25)-sin25cos20=sin25cos20-sin25cos20=0
    b)cos(π/2-7π/18)*cos(π/2-4π/9)-sin7π/36*sin5π/36=
    sin7π/18*sin4π/9-sin7π/36*sin5π/36=2sin7π/36cos7π/36sin4π/9-sin7π/36*sin5π/36=
    sin7π/36(2cos7π/36sin4π/9-sin5π/36)=                                                                      sin7π/36(2*1/2sinπ/4+2*1/2sin23π/36-sin5π/36)=sin7π/36(√2/2+sin23π/36-sin5π/36)=
    sin7π/36(√2/2+2sinπ/2cos7π/9)=sin7π/36(√2/2+2cos7π/9)=√2/2sin7π/36+
    2sin7π/36*cos7π/9=√2/2sin7π/36+2*1/2sin(-7π/12)+2*1/2sin37π/9=
    √2/2sin7π/36-sin7π/12+sin(π+π/36)=√2/2sin7π/36-sin7π/12-sinπ/36