Respostas

2013-09-23T12:43:28-03:00
F(-1) = a*-1 + b = 3
-a + b = 3 (I)
f(1) = a*1 + b = -1
a + b = -1 (II)
somando (I) + (II)
a-a + b+b = 3-1
2b = 2 ==> b = 1 subst. em (I)
a = -2
f(x) = -2x + 1 portanto
f(3) = -2*3 + 1 = -5 (resp)