-3a^2-6ab-3b^2=-3(a^2-2ab-b^2)=-3(a-ab-b)(a+ab+b)
1) 6x=10
x=10/6=5/3
2) 9x-8y=35
2x-4y=10(домножаем на -2)
8х-8у=35
-4х+8у=-20
Добавляем
4х=15
Х=15/4
6 - 2X + 15 - 3X = - 5X + 21
при Х = ( - 0.2)
- 5* ( - 0.2) + 21 = 1 + 21 = 22 (ОТВЕТ)
1)tgx=0⇒x=πn
2)sin2x=-1/2⇒2x=(-1)^n+1 *π/6+πn⇒x=(-1)^n+1 *π/12+πn/2
3)tgx/4=1⇒x/4=π/4+πn⇒x=π+4πn
4)9cosx=sinx
9cos²x/2-9sin²x/2-2sin²/2cosx/2=0 /cos²x/2≠0
9tg²x/2+2tgx/2-9=0
tgx/2=a
9a²+2a-9=0
D=4+324=328 √D=2√82
a1=(-2-2√82)/18=-(1+√82)/9⇒tgx/2=-(1+√82)/9⇒x=-2arctg(1+√82)/9+πn
a2=(-2+2√82)/18=(-1+√82)/9⇒tgx/2=(-1+√82)/9⇒x=2arctg(-1+√82)/9+πn