代数表达式

问题2:如果' p = - 2 '，求出的值:

(a) 4p + 7

答:' 4p + 7 = 4xx (- 2) + 7 '

' = - 8 + 7 = - 1 '

(b)' - 3p²+ 4p + 7 '

答:' - 3p²+ 4p + 7 '

' = - 3 × (- 2)^2 + 4 × (- 2) + 7 '

' = - 3 × 4 - 8 + 7 = 12 - 8 + 7 = 11 '

(c)- 2p^3 - 3p^2 + 4p + 7 '

答:- 2p^3 - 3p^2 + 4p + 7 '

' = - 2 × - 2^3 - 3 × (- 2)^2 + 4 × (- 2) + 7 '

' = (- 2) × (- 8) - 3 × 4 - 8 + 7 '

' = 16 - 12 - 8 + 7 = 3 '

问题3:求下列表达式的值，当' x = - 1 '时:

(一)' 2x - 7 '

答:' 2x - 7 = 2 xx (- 1) - 7 '

' = - 2 - 7 = - 9 '

(b)' - x + 2 '

答:' - x + 2 = - (- 1) + 2 = 1 + 2 = 3 '

(c)' x²+ 2x + 1 '

答:' x^2 + 2x + 1 = - 1^2 + 2 × (- 1) + 1 '

' = 1 - 2 + 1 = 0 '

(d)' 2x^2 - x - 2 '

答:' 2x^2 - x - 2 '

' = 2 × (- 1)^2 - (- 1) - 2 '

' = 2 + 1 - 2 = 1 '

问题4:如果' a = 2 '， ' b = - 2 '，求以下值:

(一)a^2 + b^2

答:' a²+ b²' = 2²+(- 2)²'

' = 4 + 4 = 8 '

(b)' a²+ ab + b²'

答:' a²+ ab + b²'

' = 2^2 + 2 × (- 2) + (- 2)^2 '

' = 4 - 4 + 4 = 4 '

(c)a^2 - b^2

答:' a²- b²= 2²-(- 2)²' = 4 - 4 = 0 '

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问题5:当' a = 0 '， ' b = - 1 '时，找出给定表达式的值:

(一)“2a + 2b”

答:' 2a + 2b = 0 + 2 xx (- 1) = - 2 '

(b)' 2a²+ b²+ 1 '

答:' 2a²+ b²+ 1 '

' = 0 +(- 1)²+ 1 = 1 + 1 = 2 '

(c)' 2a^2b + 2ab^2 + ab '

答:' 2a^2b + 2ab^2 + ab '

' = 0 + 0 + 0 = 0 '

(d)a^2 + ab + 2

答:' a^2 + ab + 2 = 0 + 0 + 2 = 2 '

问题6:化简表达式，求x = 2时的值。

(一)' x + 7 + 4 (x - 5) '

答:' x+ 7 + 4 (x - 5) '

' = 2 + 7 + 4 (2 - 5) '

' = 9 + 4 × (- 3) = 9 - 12 = - 3 '

(b)' 3(x + 2) + 5x - 7 '

答:' 3(x + 2) + 5x - 7 '

' = 3 (2 + 2) + 5 × 2 - 7 '

' = 3 × 4 + 10 - 7 = 12 + 3 = 15 '

(c)' 6x + 5(x - 2) '

答:' 6x + 5(x - 2) '

' = 6 × 2 + 5 (2 - 2) '

' = 12 + 0 = 12 '

(d)' 4(2x - 1) + 3x + 11 '

答:' 4(2x - 1) + 3x + 11 '

' = 4 (2 × 2 - 1) + 3 × 2 + 11 '

' = 4 (4 - 1) + 6 + 11 '

' = 4 × 3 + 17 = 12 + 17 = 29 '

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