3)
5^(7-2x)>=125
5^(7-2x)>=5^3
7-2x>=3
-2x>=-4
2x<=4<br>x<=2<br>4) log2,4(x-1)-log2,4(1/2)=log2,4(2)
log2,4(x-1)=log2,4(2)+log2,4(1/2)
log2,4(x-1)=log2,4(2*1/2)
log2,4(x-1)=log2(1)
x-1=1
x=2
5) (sina-cosa)^2 = 1-sin2a
sina^2-2sinacosa+cosa^2=1-sin2a
1-2sinacosa=1-sin2a
1-2sin2a=1-sin2a
ч.т.д.