If the function f(x) is defined for all real numbers x as th

If the function f(x) is defined for all real numbers x as the maximum value of 2x + 4 and 12 + 3x,then
for which one of the following values of x will f(x) actually equal 2x + 4
(A) –4
(B) –5
(C) –6
(D) –7
(E) –9
17.f(x) equals the maximum of 2x + 4 and 12 + 3x.Hence,the question asks for which value of x is 2x + 4
is greater than or equal to 12 + 3x.(Note:By symmetry,we could also ask for which value of x is 12 + 3x is
greater than or equal to 2x + 4.) Expressing the inequality yields 2x + 4 􀀂 12 + 3x.Subtracting 12 + 2x from
both sides yields x 􀀁 –8.The answer is (E) since it is the only answer-choice that satisfies the inequality.
上面是这题的解释和答案,我不太明白的是为什么说一个函数是两个表达式的最大值,就是问一个比另一个大呢?