✔ 最佳答案
f(2x-7)=8x+20,求f(x)=?
Sol
Set y=2x-7
2x=y+7
8x=4y+28
8x+20=4y+48
x=(y+7)/2
f(2x-7)=8x+20
f(y)=4y+48
f(x)=4x+48
2012-07-21 17:23:30 補充:
f(2x-7)=8x+20
設 f(x)=ax+b
when x=0
f(-7)=8*0+20=20
f(-7)=-7a+b=20................
when x=1
f(-5)=8*1+20=28
f(-5)=-5a+b=28.................
(-7a+b)-(-5a+b)=20-28
-2a=-8
a=4
b=20+7a=20+28=48
f(x)=4x+48