Question

Calculati sumele:
a) 1+2+3+...+20

b)1+2+3+...+100

c)2+4+6+...+100

d)1+4+7+10+...-37

e)5+10+15+...+100


dau coroana si 20 puncte​

Answer 1

Răspuns:

a) 20×21÷2= 10×21= 210

b) 100×101÷2= 50×101= 5050

c) 2(1+2+3+...+50)= 2×50×51÷2= 50×51= 2550

d) 1+4+7+...+37=

nr termeni: (37-1)÷3+1= 36÷3+1= 12+1= 13

Suma: (37+1)×13÷2= 38×13÷2= 19×13= 247

e) 5+10+15+...+100= 5(1+2+3+...+20)= 5×20×21÷2= 5×10×21= 5×210= 1050