Question

Care este diferenta celor doua sume ( 1+2+3+.....+56) - (1+2+3+.......+36)=?

Answer 1

$(1+2+...+56)-(1+2+...+36)= \frac{56*57}{2}- \frac{36*37}{2}= \frac{56*57-36*37}{2}=$$\frac{3192-1332}{2}= \frac{1860}{2}=930.$