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Sn=(a1+an)*n/2
n=(x+3)/4
190=((1+x)*(x+3)/4)/2
190=(x+3+x^2+3x)/4)*1/2
190=(x^2+4x+3)/8 |*8
x^2+4x+3=1520
x^2+4x-1517=0
delta=6084
√delta=78
x1=(-4-78)/2=-82/2=-41 odpada bo ujemne
x2=(-4+78)/2=37
Odp: x=37