1)3,5*4,4=15,4
2)15,4-3,4=12
3)12+3,5=15,5
4)15,5*3,5=54,25
5)31,5:1,4=22,5
6)22,5-54,25=-31,75
Sin21x*cos14x=1
sin21x=1⇒21x=π/2+2πn,n∈z⇒x=π/42+2πn/21,n∈z
cos14x=1⇒14x=2πk,k∈z⇒x=πk/7,k∈z
k=1/6+7n,n∈z
(1+2sin a cos a )/ (sin a + cos a)=(sin² a + cos² a+2sin a cos a )/(sin a + cos a)=
= (sin a + cos a)²/ (sin a + cos a)=sin a + cos a
=3x2+5x-1=x2-4x
3x2+5x-1-x2+4x=o
2x2+9x-1=o
<span> 5,3 < 6 7 8 9< 9,4
6+7+8+9=30</span>