Question

Se considera numerele a=1+2=3+..........+10
b=2+4+6+.........+20
Aratati ca b=2*a

Answer 1

a=1+2+3+...+10
b=2+4+6+8+...20=2(1+2+3+...+10)=2*a

Answer 2

$\displaystyle 1+2+3+...+10= \frac{10(10+1)}{2} = \frac{10 \times 11}{2} = \frac{110}{2} =55 \\  \\ \boxed{a=55} \\ \\ 2+4+6+...+20=2(1+2+3+...+10)=2 \times \frac{10(10+1)}{2} = \\ \\ =2 \times \frac{10 \times 11}{2} -\not2 \times \frac{110}{\not2} =110 \\ \\ \boxed{b=110} \\ \\ b=2 \cdot a \\ 110=2 \cdot 55 \\ 110=110$