Question

Stabiliți paritatea sumelor:
a. S1= 2+4+6+......+198;
b. S2= 1+3+5+......+175;
c. S3= 5+9+13+......+101;
d. S4= 5+10+15+......+85;
AJUTOR PLS​

Answer 1

Explicație pas cu pas:

S1= 2*(1+2+...+99)=2*(99*100)÷2=99*100=9900

S2=(1+2+3+....+175)-(2+4+6+...+174)=175*176÷2-2*(1+2+3+....+87)= 30800÷2-2*87*88÷2=15400-7656=7744

S3=(1+4)+(2+4)+....+(97+4)=4*97 + (1+2+...+97)= 388+97*98÷2=388+4753=5141

S4=5*(1+2+....+17)=5*17*18÷2=765