1) 1,4 : 7 = 0,2
2) ( 10 ^ 2 ) : ( 10 ^ - 1 ) = 10 ^ ( 2 - ( - 1 )) = 10 ^ 3
3) 0,2 * ( 10 ^ 3 ) = 0,2 * 1000 = 200
3x⁵y²+15x⁴y³+12x³y⁴=3x³y²(x²+5xy+4y²)=3x³y²(x²+xy+4xy+4y²)=
=3x³y²(x(x+y)+4y(x+y))=3x³y²(x+y)(x+4y)
Y=π/2-x
siny=sin(π/2-x)=cosx
x+y=π/2
sin²x-sin²y=1 или sin²x-cos²x=-(cos²x-sin²x)= - cos2x=1
cos2x= -1 2x=π+2πk
x=π/2+πk k∈Z
y=π/2-π/2-πk = -πk k∈Z
Cos²a=1:(1+tg²a)=1:(1+4)=1/5
cosa=1/√5
sina=√(1-cos²a)=√(1-1/5)=2/√5
cos2a=cos²a-sin²a=1/5-4/5=-3/5
sin2a=2sinacosa=2*1/√5*2/√5=4/5
tg2a=sin2a/cos2a=-2/3
(2+3)/(6+8)-(13-2)/(-6-12)=5/14+11/18=(45+77)/126=122/126=61/63