How do you put f(-1)=3 and f(2)=9 into the form f(x)=mx+b?

Question

I was absent one class and I must've missed something important because this doesn't make much sense to me. If I could get help today, it would be greatly appreciated.

Answer 1

Since f(x)=y , you can use rewrite f(-1)=3 and f(2)=9 as (-1,3) and (2,9). Once you have two points on a line, writing the equation of the line is easy.

Step 1: Find the slope of the line between the two points.

Step 2: Choose either point, plug it into the slope intercept equation, and solve for b.

Step 3: Rewrite your equation.

Step 1:

m = (9-3)/(2- -1) = 6/3 = 2

Step 2:

y=mx+b

3=2(-1)+b

3=-2+b

5=b

Step 3:

y = 2x + 5

f(x) = 2x + 5

Answer 2

f(-1) = 3 represents the point (-1, 3)

f(2) = 9 represents the point (2, 9)

Use the two-point form

(y - 3) / (x + 1) = (3 - 9) / (-1 - 2)