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Aratati ca [tex]sin(3 \pi /2+x)-sin(3 \pi /2-x)=0[/tex] pentru orice x∈ R .

Răspuns :

sin(3π/2*cosx+cos3π/2sinx-(sin3π/2cosx-cos3π/2*sinx)=
-cosx+0-(-1*cosx-0)=-cosx+cosx=0
sin(3π/2 +x) -sin(3π/2 -x)=0
sin3π/2*cosx+sinx*cos3π/2-sin3π/2*cosx+sinx*cos3π/2=0
-cosx+0+cosx+0=0
 -cosx si cosx se reduc
=> 0=0 (Adevarat)
3
π/2= 3*180/2= 270