中二數學問題求幫忙(5點)

銀

2012-07-27 8:25 pm

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

回答 (1)

用戶2053

2012-07-27 9:41 pm

✔ 最佳答案

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.

👍 0 👎 0