Question

Aflati termenul necunoscut din:(4+6+8+....+90)+x=3+5+7+.....+91

Answer 1

(4+6+8+.........+90)+x=3+5+7+........+91

4+6+8+.......+90=2×(2+3+4+.......+45)|+1

=2×(1+2+3+4+....+45)

=[2×(45×46):2]-1

=(45×46)-1

=2070-1

=2069

3+5+7+.......+91|+1

S=1+3+5+7+......+91

S=91+89+87+...+1

______________

2S=92+92+92+....+92

=>92 se repeta de 46 de ori

2S=92×46

2S= 4232|:2

S= 2116

2069+x=2116

×=2116-2069

x=47