(а+5)²+а(10-а)=а²+10а+25+10а-а²=20а+25
3х-3-2х+12=4-х-3
3х-2х+х=4-3+3-12
2х=-8
Х=-4
Ответ : х=-4
Оформляли бы нормально. А то пока поймешь что к чему....
![sin2\alpha cos^32\alpha - sin^32\alpha cos2 \alpha = sin2\alpha cos2 \alpha(cos^22\alpha - sin^22\alpha) = \\ = \frac{2}{2}sin2\alpha cos2 \alpha(cos^22\alpha - sin^22\alpha) =\\ = \frac{sin4\alpha}{2}(cos^22\alpha - sin^22\alpha) = \frac{sin4\alpha cos4\alpha}{2} = \frac{sin8\alpha}{4}](https://tex.z-dn.net/?f=sin2%5Calpha+cos%5E32%5Calpha+-+sin%5E32%5Calpha+cos2+%5Calpha+%3D+sin2%5Calpha+cos2+%5Calpha%28cos%5E22%5Calpha+-+sin%5E22%5Calpha%29+%3D+%5C%5C+%3D+%5Cfrac%7B2%7D%7B2%7Dsin2%5Calpha+cos2+%5Calpha%28cos%5E22%5Calpha+-+sin%5E22%5Calpha%29+%3D%5C%5C+%3D+%5Cfrac%7Bsin4%5Calpha%7D%7B2%7D%28cos%5E22%5Calpha+-+sin%5E22%5Calpha%29+%3D+%5Cfrac%7Bsin4%5Calpha+cos4%5Calpha%7D%7B2%7D+%3D+%5Cfrac%7Bsin8%5Calpha%7D%7B4%7D)
3log7x больше или равно 6
log7 x>=2
x>=49
{4-x>0
{x+5>0
{-x>-4
{x>-5
{x<4
{x>-5
\\\\\\\\\\\\\\\\\\\\\\\\\\\\
--------- -5 ------------- 4 --------------
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
x∈(-5; 4)
Длина интервала: 4- (-5) =4+5=9
Середина интервала: 9: 2=4,5
Ответ: 4) 4,5.