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แบบฝกหัดที่ 4

1. จงทําใหเปนผลสําเร็จ
1. (-12) – 7 4. (-5) – (-8)

วิธีทํา (-12) – 7 = (-12) + (-7) วิธีทํา (-5) – (-8) = (-5) + 8

= - 19 = 3

2. 7 – (-12) 5. [8 – (-2)] – 6

วิธีทํา 7 – (-12) = 7 + 12 วิธีทํา [8 – (-2)] – 6 = [ 8 + 2] + (-6)

= 19 = 10 + (-6)
= 4

3. (-8) – (-5) 6. 8 – [(-2) – 6]

วิธีทํา (-8) – (-5) = (-8) + 5 วิธีทํา 8 – [(-2) + (-6)] = 8 – (-8)

= -3 = 8 + 8
= 16

2. จงหาคาของ a – b และ b – a เมื่อกําหนด a และ b ดังตอไปนี้
1. a = 5, b = (-3)

วิธีทํา a – b = 5 – (-3) b – a = (-3) – 5

= 5 + 3 = (-3) + (-5)
= 8 = -8

2. a = (-14), b = (-6)
วิธีทํา a – b = (-14) – (-6) b – a = (-6) – (-14)

= (-14) + 6 = (-6) + 14

= (-8) = 8

3. a = (-4), b = (-4)

วิธีทํา a – b = (-4) – (-4) b – a = (-4) – (-4)

= (-4) + 4 = (-4) + 4
= 0 = 0