1)a+b=31
a,b-varsta celor 2 surori x-anii peste care cele 2 surori vor avea impreuna 39 de ani
a+x+b+x=39
31+2x=39
2x=39-31
2x=8
x=4
2)( √10 * √90:√50)² -(√90 -√40)²= (√900 :√50) -( 90 -2√360 +40)=
=(√18)² -(130 -2*60)=
=18 -(130-120)=
=18 -10=8
3)a=√3⁴ +3⁵= √3⁴(1+3)= 3² √4= 3² *2=9*2=18
4)D (-4)= { -1;1; -2;2;-4;4}