Ах^2+bx^2-bx-ax+a+b=(ах^2-ax+a)+(bx^2-bx+b)=a(х^2-x+1) + b(х^2-x+1)=(х^2-x+1)(a+b)
(6n+7n)^2 = 36m^2 + 84mn + 49n^2
51^2 = 51*51 = 2601
((19/20)19)^2 = 399/20
{3-4x>0⇒3>4x⇒x<3/4
{3-4x<3⇒-4x<0⇒x>0
x∈(0;0,75)
{3а–7b=8 |•(-2)
{6a–5b=–2
{–6a+14b=–16
{6a–5b=–2
9b=–18
b=–2
6a–5•(-2)=–2
6a=–12
a=–2
Решение вложила, удачи:)))))