<span>Cos2а=0,2</span><span>
Cos^2a=(1+Cos2a)/2=(1+0.2)/2=0.6 <u>Cosa=√0.6</u></span><span>
Sin^2a=1- Cos^2a
=1-0.6=0.4 <u>Sina= √0.4</u></span>
tga= Cos^a/
Sin^a= √1.5
Используя теорему Виета можно подобрать корни: с=-7*(-13)=91 и
-b=-7+(-13)=-20⇒b=20
Ответ:-7; -13.
![\frac{1}{a^{ \frac{1}{3} }-b^{ \frac{1}{3} }} - \frac{a^{ \frac{2}{3}}+b^{ \frac{2}{3} }}{(a^{ \frac{1}{3} }-b^{ \frac{1}{3}} )*(a^{ \frac{2}{3} }+a^{ \frac{1}{3} }*b^{ \frac{1}{3} }+b^{ \frac{2}{3} })}](https://tex.z-dn.net/?f=+%5Cfrac%7B1%7D%7Ba%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D-b%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D%7D+-+%5Cfrac%7Ba%5E%7B+%5Cfrac%7B2%7D%7B3%7D%7D%2Bb%5E%7B+%5Cfrac%7B2%7D%7B3%7D+%7D%7D%7B%28a%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D-b%5E%7B+%5Cfrac%7B1%7D%7B3%7D%7D+%29%2A%28a%5E%7B+%5Cfrac%7B2%7D%7B3%7D+%7D%2Ba%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D%2Ab%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D%2Bb%5E%7B+%5Cfrac%7B2%7D%7B3%7D+%7D%29%7D+)
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![\frac{a^{ \frac{1}{3} }*b^{ \frac{1}{3} }}{a-b}](https://tex.z-dn.net/?f=+%5Cfrac%7Ba%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D%2Ab%5E%7B+%5Cfrac%7B1%7D%7B3%7D+%7D%7D%7Ba-b%7D+)
X - 2Y = - 2
X - 4Y = - 6
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X - 2Y = - 2
- X + 4Y = 6
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6Y = 4
Y = 2/3
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X - 4/3 = - 2
X = - 2 + 4/3 = = - 1 3/3 + 1 1/3 = 2/3
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Ответ ( 2/3 ; 2/3 )