Question

1+3+5+7+9+...+19=?
Urgeeent!
Dau coroană

Answer 1

1+3+5+7+....+17+19 = (1+19) +(3+17) +(5+15)+(7+13)+(9+11) = 20 x 5 = 100

sau

1+3+5+.....+19 = (1+19)x10/2 = 200/2 = 100

Answer 2

$\boxed{1+3+5+...+n = \left(\dfrac{n+1}{2}\right)^2} \rightarrow \text{formul\u{a}}\\ \\ \\ \text{Aplic\u{a}m formula:}}\\ \\ \Rightarrow 1+3+5+...+19 = \left(\dfrac{19+1}{2}\right)^2 = \left(\dfrac{20}{2}\right)^2 = 10^2 = 100$