1)cosa=-4/5
sina=√(1-cos²a)=√(1-16/25)=√(9/25)=3/5
tga=sina/cosa=3/5:(-4/5)=-3/5*5/4=-3/4
cos2a=cos²a-sin²a=16/25-9/25=7/25
2)cos135=cos(180-45)=-cos45=-√2/2
sin8π/3=sin(3π-π/3)=sin(π-π/3)=sinπ/3=√3/2
<span>y=</span>√(<span>x+20-x^2)
x+20-x2</span>≥0
-x2+x+20≥0
<u>x2-x-20≤0</u>
x2-x-20=0
D=1+80=81
x(1)=(1+9)/2=5
x(2)=(1-9)/2=-4
график парабола ветви вверх
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-4 5
Ответ: х∈[-4; 5]
<span>6x-4y=10
6x=10+4y
x=10/6 +4/6 y
x=5/3+2/3 y
x=5/3 +2/3 y
</span><span>11+3y=39
3y=39-11
3y=28
y=28/3
y=9 1/3 =9.3333
</span>