Explicație pas cu pas:
S1=1+2+3+...+101=101*102/2=101*51
=>51/101*51=2/x=>1/101=2/x=>x=101*2=202
S2=11+12+13+...+120
n=(120-11)/1+1=109+1=110 (nr de termeni)
S2=(120+11)*n/2=131*110/2=131*55
131*55/x=131/5 => 55/x=1/5 => x=55*5=275
b)51•X=2•(1+2+3+...+101)
51•X=2•(101•102)/2
51•X=2•5151
51•X=10302
X=10302÷51
X=202
c)X•131=5•(11+12+13+...+120)
X•131=5•(120×121)/2
X•131=5•7260
X•131=36300
X=36300÷131
X=277,09
☆Sper că te-am ajutat!☆
