[tex]\it a)\ \ = 1+2+3+\ ...\ +50=\dfrac{50\cdot51}{2}=25\cdot51=\\ \\ \\ b)\ \ = 3+6+9+\ ...\ +90=3(1+2+3+\ ...\ +30)=3\cdot\dfrac{30\cdot31}{2}=3\cdot15\cdot31=[/tex]
Răspuns:
Explicație pas cu pas:
