Hướng dẫn Giải Bài 7.5 (Trang 36, SGK Toán 6, Tập 2, Bộ Kết Nối Tri Thức)

Tính: a) (-12,245) + (-8,235) b) (-8,451) + 9,79 c) (-11,254) - (-7,35) Giải: a) (-12,245) + (-8,235) = -(12,245 + 8,235) <math xmlns="http://www.w3.org/1998/Math/MathML"><mo> </mo><mo> </mo><mn>12</mn><mo>,</mo><mn>245</mn><mspace linebreak="newline"/><mo>+</mo><mn>8</mn><mo>,</mo><mn>235</mn><mspace linebreak="newline"/><mover><mrow><mo> </mo><mo> </mo><mn>20</mn><mo>,</mo><mn>480</mn></mrow><mo>¯</mo></mover></math> <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⇒</mo></math>(-12,245) + (-8,235) = -20,48 b) (-8,451) + 9,79 = 9,79 - 8,451 <math xmlns="http://www.w3.org/1998/Math/MathML"><mo> </mo><mo> </mo><mo> </mo><mo> </mo><mn>9</mn><mo>,</mo><mn>79</mn><mspace linebreak="newline"/><mo>-</mo><mn>8</mn><mo>,</mo><mn>451</mn><mspace linebreak="newline"/><mover><mrow><mo> </mo><mo> </mo><mo> </mo><mo> </mo><mn>1</mn><mo>,</mo><mn>339</mn></mrow><mo>¯</mo></mover></math> Vậy (-8,451) + 9,79 = 1,339 c) (-11,254) - (-7,35) = -(11,254 - 7,35) <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>11</mn><mo>,</mo><mn>254</mn><mspace linebreak="newline"/><mo>-</mo><mn>7</mn><mo>,</mo><mn>350</mn><mspace linebreak="newline"/><mover><mrow><mo> </mo><mo> </mo><mo> </mo><mn>3</mn><mo>,</mo><mn>904</mn></mrow><mo>¯</mo></mover></math> Vậy (-11,254 ) - (-7,35) = -3,904