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12=2*2*3
14=2*7
НОК(12,14)=2*2*3*7=84
(4x - 3y)^2 - (2x + y)(3x - 5y)
(16x^2 - 24xy + 9y^2) - (6x^2 - 10xy + 3xy - 5y^2)
16x^2 - 24xy +9y^2 - 6x^2 + 10xy - 3xy + 5y^2
10x^2 + 14y^2 - 17xy
10x^2 - 17xy + 14y^2
<u>Ответ: 10x^2 - 17xy + 14y^2</u>
Думаю так..............................
1)2-2сos²x-5cosx+1=0
2cos²x+5cosx-3=0
cosx=a
2a²+5a-3=0
D=25+24=49
a1=(-5-7)/4=-3⇒cosx=-3<-1 нет решения
a2=(-5+7)/4=1/2⇒cosx=1/2⇒x=+-π/6+2πn,n∈Z
2)sin2x+cos2x=0/cos2x≠0
tg2x+1=0⇒tg2x=-1⇒2x=-π/4+πn.n∈Z⇒x=-π/8+πn/2,n∈Z