Question

A line passes through (4, 5) and (8, 9). Which equation best represents the line?

y = 5x + 8
y = 2x + 1
y = x + 1
y = 1

Answer 1

Write them as functions, replace y with f(x). And substitute x with its coordinate value.

Answer 2

y = f(x); solve to get the value y.

Answer 3

im confused
haha

Answer 4

@phi

Answer 5

Example: y = 5x + 8
f(x) = 5x + 8
Substitute x. Since coordinates are (x, y), Either substitute x with 4 and see if the equation give out 5 or substitute x with 8 and see if the equation give out 9. Find the equation that agrees with the ordered pair.

Answer 6

y = f(x)

Answer 7

you could test if each point "works" in the choices.
Only one of the choices will work.

For example, the last choice y=1 means no matter what x is , y will be 1
Do your points have y=1 ?

Answer 8

yes?

Answer 9

D?

Answer 10

when they give you a point like
(4, 5)
that is a point at x=4 and y=5
it's y value is 5. 5 is not 1.

Answer 11

ohhhhhh i get it now

Answer 12

so it would be A

Answer 13

right?

Answer 14

f(x) = y

Answer 15

so far , you know y=1 is NOT correct (because the second number in your points is not 1)

Answer 16

yea.

Answer 17

to check choice A
y = 5x + 8

use point (4,5) , that means x=4
replace x (erase it, and put in 4 ) in
y = 5x + 8
then simplify
can you do that ?

Answer 18

13x

Answer 19

if you replace x with 4, there won't be an "x" in the answer
try again.
replace x (erase it, and put in 4 ) in y = 5x + 8

Answer 20

oh 5x4+8?

Answer 21

yes, but use * for multiply (because using x is confusing)
now use order of operations. do the multiply first, then add

Answer 22

ok so it would be 28?

Answer 23

yes. what you did is use the equation
y= 5x+8
this equation says, "if x is 4, then you get y=28"

now your point is (4,5)
the point has a y=5

5 is not 28
so this is the WRONG equation.
so far we crossed of A and D

two more to check

Answer 24

okay

Answer 25

I think its B

Answer 26

which choice do you want to check ?

Answer 27

B

Answer 28

y = 2x + 1
let's use (4,5) again. when x=4 we want to get y=5

can you test x=4 in
y = 2x + 1

Answer 29

=9

Answer 30

replace x with 4 in
y = 2x + 1
can you do that ?

Answer 31

=9

Answer 32

right?
I dont know if i am doing this wrong or something?

Answer 33

@phi