Б)(1,2-a)(1.2+a)=1.2²-a²;
г)(1/5·a-3/7·b)(14a+b)=14/5a²-14·3/7·ab+1/5ab-3/7b²=2.8a²-5.8ab-3/7b²;
e) (2.5a+3b)(0.1b-4a)=0.25ab+0.3b²-10a²-12ab=0.3b²-11.75ab-10a²;
з)(1¹/₂x-y)(2¹/₃y-¹/₃x)=(³/₂x-y)(⁷/₃y-¹/₃x)=²¹/₆xy-⁷/₃y²-³/₆x²+¹/₃xy=²³/₆xy-⁷/₃y²-¹/₂x₂
cos(x)<√3/2
x=-11pi/6+2pik
x=-pi/6+2pik
x=(<span>-11pi/6+2pik;<span>pi/6+2pik) . k=z</span></span>
<span><span> cos(x)≥-1/2</span></span>
<span><span>x=2pi/3+2pik</span></span>
<span><span>x=-2pi/3+2pik</span></span>
<span><span>x=(-2<span><span>pi/3+2pik;2pi/3+2pik) . k=z</span></span></span></span>
Общее:x=[-2pi/3+2pik;-pi/6+2pik)U(pi/6+2pik;2pi/3+2pik] / k=z
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cos(x)≥0
x=pi/2+2pik
x=-pi/2+2pik
x=[-pi/2+2pik;pi/2+2pik] . k=z
sin(x)<-√2/2
x=-3pi/4+2pik
x=-pi/4+2pik
x=(-3pi/4+2pik;-pi/4+2pik) . k=z
Общее: x=[-pi/2+2pik;-pi/4+2pik) . k=z
1)70:35=2 т/час
2)70:14=5 т/час
3)2+5=7т/час
4)7<span>0:7=10 часов
</span>Ответ:за 10 ч<span>
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