У = 6х -12 = 18
у = 18
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6х - 12 = 18
6х = 18 + 12
6х = 30
х = 5
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у = 6*5 - 12
у = 30 - 12
у = 18
1)у2+15*15+2*15*у
2)25х2+0,2*0,2-2*5х*0,2
3)4а2+49b2+2*-2a*7b
4)a9+a16+2*a3*a4
Sinx=√2/2
x=(-1)^k×arcsin(√2/2)+πk k∈Z
arcsin(√2/2)=π/4
x=(-1)^k×π/4+πk k∈Z
cos840=cos(360+360+120)=cos120=-cos60=-0.5
(а-1)³+8а⁶ = (а-1)³+(2а²)³ = ((а-1)+2а²)((а-1)²-(а-1)*2а²+(2а²)²) = (а-1+2а²)(а²-2а+1-2а³+2а²+8а⁴) = (2а²+а-1)(8а⁴-2а³+3а²-2а+1)