a) - 9 / 5 + 37 / 10 - 38 / 15 = ( - 54 + 111 - 76 ) / 30 = - 19 / 30
→ cmmmc al numitorilor ( 5; 10 si 15 ) = 2 x 3 x 5 = 30
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b) - 25 / 21 + 16 / 7 - 45 / 14 = ( - 25 × 2 + 16 × 6 - 45 × 3 ) / 42 =
= ( - 50 + 96 - 135 ) / 42 = 89 / 42 = 2 intregi si 5 / 42
→ cmmmc al numitorilor 21; 7 si 14 = 2 x 3 x 7 = 42
→ aduc fractiile la acelasi numitor
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c) - 16 / 45 - 8 / 27 - 25 / 36 + 41 / 54 = ( - 16 × 12 - 8 × 20 - 25 × 15 + 41 × 10 ) / 540 =
= ( - 192 - 160 - 375 + 410 ) / 540 =
= ( - 727 + 410 ) / 540 =
= - 317 / 540
45 = 3² × 5
27 = 3³
36 = 2² × 3²
54 = 2 × 3³
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cmmmc = 2² × 3³× 5 = 4 × 27 × 5 = 540
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d)
- 13 / 42 + 9 / 56 - 8 / 63 + 5 / 84 =
= ( - 13 × 12 + 9 × 9 - 8 × 8 + 5 × 6 ) / 504 =
= ( - 156 + 81 - 64 + 30 ) / 504 =
= - 109 / 504
42 = 6 x 7 = 2 x 3 x 7
56 = 8 x 7 = 2³ x 7
63 = 7 x 9 = 7 × 3²
84 =7 x 4 x 3 = 2² × 3 × 7
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cmmmc al numitorilor ( 42; 56; 63; 84 ) = 7 x 8 x 9 = 504
