1、GRE（ QUANTITATIVE）练习试卷 22及答案与解析 1 For the function f(x)=x2-4x+8, what is the value of f(6)? 2 If f(x)=x2, find f(x+1). 3 If the function f(x)=x+2, and the function g(x)=3x, what is the function gf(x)? 4 For the function what is the value of f(2)? 5 For the function f(x)=x2+x, what is the value of f(
2、-5)? GRE（ QUANTITATIVE）练习试卷 22答案与解析 1 【正确答案】 To solve, substitute 6 for x in the function: f(6)=62-4(6)+8 f(6)=36-24+8 f(6)=20 2 【正确答案】 To solve, substitute (x+1) for x in the function: f(x+1)=(x+1) 2 (x+1)(x+1) x2+x+x+1 x2+2x+1 3 【正确答案】 The problem gives g(x)=3x and f(x)=x+2 and asks for gf(x). The function gf(x) means that all of the x values in g(x) are replaced with f(x), as follows: gf(x)=3f(x) gf(x)=3(x+2) gf(x)=3x+6 4 【 正确答案】 To solve, substitute 2 for x in the function: 5 【正确答案】 To solve, substitute -5 for x in the function: f(-5)=(-5) 2+(-5) f(-5)=25-5 f(-5)=20
