Tolong ka,aku gk ngerti bgt,besok kumpul ._.

f(x) = px + q
f(1) = p(1) + q
=> p + q = 3 ... [i]

f(2) = p(2) + q
=> 2p + q = 1 ... [ii]

Eliminasi i dan ii
p + q = 3
2p + q = 1
––––––––––– (–)
-p = 2
p = -2

Subtitusikan p = -2 ke p + q = 3
-2 + q = 3
q = 5

Jadi f(x) nya adalah
f(x) = -2x + 5

untuk x = 4
f(4) = -2(4) + 5
=>-8 + 5 = -3