5х-15=х-21х-35
25х=-20
х=-20/25=-4/5=-0,8
4x²-20x=0
4x(x-5)=0
4x=0 x-5=0
x1=0 x2=5
Начнём упрощать
Root(a*root(a^(4/3);3);3)*a^(14/27)=root(a^(13/9);3)*a^(14/27)=a^(13/27)*a^(14/27)=a
<span>4x^2−5x+12 = <span><span>3x^2+8x−30</span></span></span>
<span>x^2-13x+42 = 0 </span>
<span>По теореме Виета:</span>
<span>x1+x2 = 13</span>
<span>x1*x2 = 42 </span>
<span>x1 = 6, x2 = 7 </span>
<span>f(6) = 4*6^2-5*6+12 = 126 (6;126)
</span>
<span>f(7) = 3*7^2 +8*7 -30 = 173 (7;173)</span>
<span>Ответ: <span>(6;126)</span>, <span>(7;173)</span>, 173.</span>
Во втором задании у Вас ошибка.