Решение
81у^2-36xy-60x^2 = (81y² - 36xy + 4x²) - 4x² - 60x² =
= (9y - 2x)² - 64x² = (9y - 2x - 8x)*(9y - 2x + 8x) =
= (9y - 10x)*(9y + 6x) = 3*(<span>9y - 10x)*(3y + 2x)</span>
sin2xcos2x=-1/4
2•sin2xcos2x=-1/4*2
sin4x=-1/2
4x=(-1)^narcsin(-1/2)+πn
4x=(-1)^(n+1)arcsin1/2+πn
4x=(-1)^(n+1)•π/6+πn
x=(-1)^(n+1)π/24+πn/4;n€Z
X^2+px-28=0
x1=7
49+7p-28=0
7p+21=0
7p=-21
p=-3
по теореме Виета:
x1+x2=-p =>x1+x2=-(-3)=3
x1*x2=q
ответ:x1+x2=3