0,5а(2а-b)-0,5b*(2b-a)=
a^2-0,5ab-b^2+0,5ab=
a^2-b^2=(a-b)(a+b)
I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...I don't no...
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
D(дискриминант)=(-10)^2-4*7*7=-96<0,значит уравнение не имеет корней и все значения одного знака,подставив любое значение переменной,например 0,получим у=7>0,что и требовалось доказать
Девочке снизу-Зачем копипастить мое решение?
<span>1/2(cosx+cos3x)=1/2(cos2x+cos3x)
cosx+cos3x=cos2x+cos3x
cosx-cos2x=0
-2sin(3x/2)sin(x/2)=0
sin(3x/2)=0⇒3x/2=πn⇒x=2πn/3
sin(x/2)=0⇒x/2=πn⇒x=2πn</span>