Question

a=1+2+3+4+......+23
b=3+6+9+12+.....+84


va rog e urgent ​

Answer 1

Salutare!

a = 1 + 2 + 3 + 4 + ... + 23

a = 23 × ( 23 + 1 ) : 2

a = 23 × 24 : 2

a = 552 : 2

a = 276

b = 3 + 6 + 9 + 12 + ... + 84

b = 3 × ( 1 + 2 + 3 + 4 + ... + 28 )

b = 3 × [ 28 × ( 28 + 1 ) : 2 ]

b = 3 × ( 28 × 29 : 2 )

b = 3 × ( 812 : 2 )

b = 3 × 406

b = 1218

Am folosit formula sumei lui Gauss:

• 1 + 2 + 3 + ... + n = n × ( n + 1 ) : 2