6. จงหาค่าของ (a – b) + c และ a – (b + c) เมื่อกำหนด a, b และ c ดังต่อไปนี้
1) a = 2 b = -5 c = 4
วิธีทำ
(a – b) + c
= [2 – (-5)] + 4
= (2 + 5) + 4
= 7 + 4
= 11
= 7 + 4
= 11
a – (b + c)
= 2 – [(-5) + 4]
= 2 – [-(5 – 4)]
= 2 – (-1)
= 2 + 1
= 3
ดังนั้น (a – b) + c = 11 และ a – (b + c) = 3
ตอบ 11, 3
ตอบ 11, 3
2) a = 3 b = -2 c = -1
วิธีทำ
(a – b) + c
= [3 – (-2)] + (-1)
= (3 + 2) + (-1)
= 5 + (-1)
= 5 – 1
= 4
= 5 + (-1)
= 5 – 1
= 4
a – (b + c)
= 3 – [(-2) + (-1)]
= 3 – [-(2 + 1)]
= 3 – (-3)
= 3 + 3
= 6
ดังนั้น (a – b) + c = 4 และ a – (b + c) = 6
ตอบ 4, 6
ตอบ 4, 6
3) a = -7 b = -7 c = -1
วิธีทำ
(a – b) + c
= [(-7) – (-7)] + (-1)
= [(-7) + 7] + (-1)
= 0 + (-1)
= -1
= 0 + (-1)
= -1
a – (b + c)
= (-7) – [(-7) + (-1)]
= (-7) – [-(7 + 1)]
= (-7) – (-8)
= (-7) + 8
= 8 – 7
= 1
ดังนั้น (a – b) + c = -1 และ a – (b + c) = 1
ตอบ -1, 1
ตอบ -1, 1