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標題:

中二數學問題求幫忙(5點)

發問:

1.determine the equation is an identity or not. (a)4x+8=17 (b)4x-6=2(2x-3) (c)(x+1)(x-5)=x^2-4x-5 (d)3(x^2-4)=3(x^2-1)-9

最佳解答:

1a) 4x + 8 = 17 4x = 9 x = 9/4Only true for x = 9/4 , so 4x + 8 = 17 is NOT an identity. b)4x - 6 = 2(2x - 3) 4x - 6 = 2*2x - 2*3 4x - 6 = 4x - 6 L.H.S.= R.H.S.So 4x - 6 ≡ 2(2x - 3) is an identity. c)(x + 1)(x - 5) = x2 - 4x - 5 x(x + 1) - 5(x + 1) = x2 - 4x - 5 x2 + x - 5x - 5 = x2 - 4x - 5 x2 - 4x - 5 = x2 - 4x - 5 L.H.S. = R.H.S.So (x + 1)(x - 5) ≡ x2 - 4x - 5 is an identity. d)3(x2 - 4) = 3(x2 - 1) - 9 3(x2 - 4) = 3(x2 - 1) - 3 * 3 3(x2 - 4) = 3(x2 - 1 - 3) 3(x2 - 4) = 3(x2 - 4) L.H.S. = R.H.S.So 3(x2 - 4) ≡ 3(x2 - 1) - 9 is an identity.

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