👤

Fie M ={x | x ∈[π/2,-π/2] si 4 |sin x| cos x = 1
Sa se afle numarul de elemente al multimii {x + y | x, y ∈ M}.


Răspuns :

x ∈ [ -π/2 , 0 ) 
-4 sinx ·cosx = - 2· 2sinx cosx = -2 ·sin2x = 1 
sin2x = -1 /2  ; 2x = -π/6 ; x = - π/12
x ∈ [0, π/2] 
4 ·sinx ·cosx = 2·2sinx cosx = 2sin2x =1 
sin2x = 1 /2      ; 2x = π/6  ; x= π/12
x +y = - π/12 + π/12 = 0