1)2sin15°cos15°=sin30°=1/2.
3)(cos75°-sin75°)²=cos²75°-2sin75°cos75°+sin²75°=1-sin150°=1-sin(180°-30°)=
1-1/2=1/2.
339.1)2sinπ/8cosπ/8=sinπ/4=√2/2.
2)sinπ/8cosπ/8+1/4=(2sinπ/8·cosπ/8) /2 +1/4=(sinπ/4)/2+1/4=√2/4+1/4=(√2+1)/4.
340.1)sinα=3/5,α∈2четв.
cosα= -√1-sin²α =-√1-9/25 = -√16/25= -4/5,(sin²α+cos²α=1)
sin2α=2sinαcosα=2·3/5·(-4/5)= -24/25.
2)cosα= -4/5,α∈3чтв.
sin2α=2sinαcosα=2·(-4/5)·(-√1-16/25)=2·(-4/5)·(-3/5)=24/25.