Question

Si: A= 1+2+3+4+....+25
B= 2+4+6+8+....+40

Determina: A+B

Answer 1

A=25(26)/2=325
B=2(20(21))/2=20(21)=420
A+B=325+420=745

Answer 2

.............................

$\displaystyle \text{Suma de los primeros } n \text{ naturales : } \frac{n(n+1)}{2} \\[4pt] \displaystyle A=1+2+3+...+25 \ \Rightarrow \ \text{hay 25 n\'{u}meros} \\[4pt] A=\frac{25(26)}{2}=325 \\[8pt] B=2+4+6+8...+40=2(1+2+3+...+20) \ \Rightarrow \ \text{hay 20 n\'{u}meros} \\[4pt] B=2\cdot \frac{20(21)}{2}=420 \\[8pt] A+B=325+420=745$