Question

se stie ca x+y=7. Calculati:

Answer 1

S=(x+y)-(2x+2y)+(3x+3y)-(4x+4y)+...+(49x+49y)-(50x+50y)=1(x+y)-2(x+y)+3(x+y)-4(x+y)+...+49(x+y)-50(x+y)=(x+y)(1-2+3-4+...+49-50)=(x+y)(-1-1-...-1)=(x+y)*(-25)=7*(-25)=-175

S=-175