linear function

Question

If f is a linear function for which
f(1) = 4
and
f(−1) = 14,
find
f(7)=?

Answer 1

f(x) is linear and passes through points (1, 4) and (-1, 14), therefore its equation is

y-4=-(10/2)(x-1)

y=-5x+9

Check it: if x=1, y=4 if x=-1, y=14

Now you can find y when x=7

f(7)=-5*7+9=-26