1)sina=-4/5
cosa=-√1-sin²a=-√1-16/25=-√9/25=-3/5
tga=sina/cosa=-4/5:(-3/5)=4/5*5/3=4/3
ctga=1/tga=1:4/3=3/4
2)tg0,3*ctg0,3=1
tg²a+tg0,3*ctg0,3=tg²a+1=1/cos²a
3)1-2sin²a=cos2a
1-2cos²a=-cos2a
sin²a+(1-2sin²a)/(1-2sin²a)=sin²a-cos2a/cos2a=sin²a-1=-cos²a
4)cost/(1+sint) +(1+sint) /cost=[cos²t+(1+sint)²]/cost(1+sint)=
=(cos²t+1+2sint+sin²t)/cost(1+sint)=(2+2sint)/cost(1+sint)=2(1+sint)/cost(1+sint)=2/cost