Jawabanmu

2014-06-22T07:20:20+07:00
(y-y1)/(y2-y1) = (x-x1)/(x2-x1)
(y-5)/(3-5) = (x-1)/(2-1)
(y-5)/-2 = (x-1)/1
y-5 = -2(x-1)
y-5 = -2x+2
y = -2x+7
f(x) = -2x + 7

f(3) = -2.3 + 7 = -6 + 7 = 1

maaf kalau salah ^^