Question

f(x 3)=-2x-6,求fx的值

Answer 1

f(x +3)=-2x-6

【解法1

令x+3=t

-2x-6=-2(x+3)=-2t

f(t)=-2t

用x替换t

f(x)=-2x

【解法2

x+3 看成整体

f(x+3)=-2(x+3)

用x替换(x+3)

f(x)=-2x