单选题For which of the following equations is x = -2 a root?I. 2/x-4II. x2 + 4=0III. x2 + 4x +4 = 0AI onlyBII onlyCIII onlyDI and IIIEII and III

单选题
For which of the following equations is x = -2 a root?I. 2/x-4II. x2 + 4=0III. x2 + 4x +4 = 0
A

I only

B

II only

C

III only

D

I and III

E

II and III

参考解析

解析：
For each Roman numeral equation, check whether -2 is a root.
I. If (2/x)-x = 0, then 2/x =x. If x = -2, then 2/x = 2/-2 = -1 ≠ x. Hence, -2 is not a root of equation I.
II. If x2+4 = 0, then (-2) 2+4 = 4+4≠ 0. Hence,-2 is not a root of equation II.
III. If x2+4x+4 = 0, then (-2) 2+4(-2)+4 = 4-8+2 = 0. Hence, -2 is a root of equation III.
Only equation III has -2 as one of its roots.

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