Răspuns: x = 8
Explicație pas cu pas:
x · ( 12+13+......+25) : 8 + 17 = 1+2+3+......+23
x · (25-12+1) · (12+25) : 2 × ( 1/8) = 23 × (1+23) : 2 - 17
x · (14 · 37 : 2 ) · (1/8) = 23 × 12 - 17
x · (7×37) · ( 1/8) = 276 - 17
x · 259 = 8 × 259 l : 259
x = 8
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12 + 13 + ...... + 25 =
( 25 - 12 ) + 1 = 13 + 1 = 14 termeni are suma
sau pot adăuga numerele de la 1 până la 11, apoi le scad:
( 1+2+3+4+......+12+.....+25) - ( 1+2+3+.....+11) =
= 25 × (1+25) : 2 - 11 × (1+11) : 2 =
= 25 × 13 - 11 × 6 =
= 325 - 66 =
= 259
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1+2+3+......+23 = 23 termeni × (1+23) : 2
→ aplic formula sumei lui Gauss
