Question

3+6+9+...+36= suma lui gauss

Answer 1

3(1+2+3+......+12)=

$S = \frac{12* \13}{2}$

  S=78;

3 * 78  =  234;

Answer 2

3×(1+2+3+...+12)= 3×(12×13:2)=3×78=234