Question

Which functions have a positive rate of change and which have a negative rate of change?

Column A

1. 2x − 5y = −15

2. y = −4x + 9

3. x y
2 –10
4 –16
6 –22

4. x y
–3 15
–2 11
–1 7

Column B
A. positive

B. negative

Answer 1

i think the 3rd one is negative and the 4th one is positive

Answer 2

@campbell_st do you know this?

Answer 3

yes... its all about the slope of the line.

if the slope is positive then the line has positive rate of change.

same for negative rate of change

Answer 4

was i right about 3 & 4
?

Answer 5

so for the 1st 2 equations may y the subject of the equation so its in the form

y = mx + b m is the slope

Answer 6

for 3 and 4 you need the slope formula so just pick to points


in 3 if I choose (4, -16) and (6, -22)

the slope is \[m = \frac{-22 -(-16)}{6 - 4}\]

does that result in a positive number.

Answer 7

yes

Answer 8

and in 4 if I pick (-3, 15) and (-1, 7)

does

\[m = \frac{15 - 7}{-3 -(-1)}\]

result in a positive or negative number.

Answer 9

negative

Answer 10

1, negative 2, positive ??