Helo everyone can someone help me to resolve this ?

If f is a linear model for which f(4) = -3 and f(-4) = 21

1. find f(9)

How do I do that ? Can someone show/ explain it to me ?

Guest Nov 1, 2015

#1**+5 **

The equation of a straight line can be written as f(x) = m*x + c where m and c are constants found from the given information as follows:

f(-4) = 21 so 21 = -4*m + c ...(1)

f(4) = -3 so -3 = 4*m + c ...(2)

Add (1) and (2) term by term to get 21 - 3 = -4m + 4m + c + c or 18 = 2c so c = 9

Put this back into (2) to get -3 = 4m + 9 so 4m = -12 so m = -3

Hence the straight line function is f(x) = -3x + 9

Now simply replace x by 9 to work out what f(9) is.

Alan Nov 2, 2015