2
(√2/2+√2/2)*1:(-1/2)=√2:(-1/2)=-√2/2
3
cosa=+-√(1-sin²a)=+-√(1-9/25)=+-√16/25=+-4/5
(1-sin²a)/3cosa=cos²a/3cosa=cosa/3=+-4/15
4
a)0+0+tg(270+30)ctg(270-30)=-ctg30*tg30=-√3*1/√3=-1
b)tg(2π-π/4)ctg(π+π/4)+tg(2π-π/6)ctg(π+π/6)=
=-tgπ/4*ctgπ/4-tgπ/6*ctgπ/6=-1*1-1/√3*√3=-1-1=-2