SOLUTION: in a linear function f(x) with a graph that has a slope of -2.5, if f(5) =8, what is the value of f(1)

Algebra ->  Functions -> SOLUTION: in a linear function f(x) with a graph that has a slope of -2.5, if f(5) =8, what is the value of f(1)      Log On


   

Question 1062860: in a linear function f(x) with a graph that has a slope of -2.5, if f(5) =8,
what is the value of f(1)
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The general form is:
+y+=+mx+%2B+b+
+m+=+-2.5+
+y+=+-2.5x+%2B+b+
---------------------
+y+=+f%28x%29+
+8+=+f%285%29+
This is the point ( 5,8 ), so
+y+=+-2.5x+%2B+b+
+8+=+-2.5%2A5+%2B+b+
+8+=+-12.5+%2B+b+
+b+=+20.5+
------------------------
The equation is:
+y+=+-2.5x+%2B+20.5+
+f%281%29+=+-2.5%2A1+%2B+20.5+
+f%281%29+=+18+
-------------------------
check:
does the line go through ( 5,8 ) ?
+y+=+-2.5x+%2B+20.5+
+8+=+-2.5%2A5+%2B+20.5+
+8+=+-12.5+%2B+20.5+
+8+=+8+
Does it go through ( 1,18 ) ?
+18+=+-2.5%2A1+%2B+20.5+
+18+=+18+
OK