Question

Calculeaza folosind factorul comun: b)3+6+9+...+90

Answer 1

b)3+6+9+...+90=

$=3*1+3*2+3*3+....+3*30=$

$=3(1+2+3+...+30)=$

$=3* \frac{30*31}{2}=$

$=3*15*31=$

$=45*31=$

$=1395$