А)
cos²π/8-sin²π/8=1-sin²π8-sin²π/8=1-2sin²π/8=
=cos(2*π/8)=cosπ/4=1/√2
б)
2*cos²15 * tg15=2*сos²15 * sin15/cos15=2*cos15 *sin15=
=sin(2*15)=sin30=1/2
2)
sina=-0,6
cos2a=1-2sin²a=1-2*(-0,6)² =1-2*0,36=1-0,72=0,28
1) = 5√(2² * 3) - 2√(4² * 3) + 2√(3² * 3) = 10√3 - 8√3 + 6√3 = 8√3
2) = 0,1√5m - √(0,3² * 5)m + 2√(4² * 5)m = 0,1√5m - 0,3√5m + 8√5m = 7,8√5m
1/sin170-√3/sin100=1/sin(180-10)-√3/sin(90+10)=
=1/sin10-√3/cos10=(cos10-√3sin10)/(sin10cos10)=
2*(1/2*cos10-√3/2*sin10)/(1/2*sin20)=4sin(30-10)/sin20=4sin20/sin20=4