Question

Let f(x) = -2x - 7 and g(x) = -4x + 3. Find (f *g)(-5)

Answer 1

f*g means multiply f by g. So do that, but don't forget to use parentheses as always.

Answer 2

(-2x-7)*(-4x+3) ? So when i take the parentheses off it all stays the same of does the four go from negative to positive? /.\

Answer 3

Keep it as is. Now you just need to plug in -5 for x, and simplify

Answer 4

ok so (-2(-5)-7)*(-4(-5)+3) right?

Answer 5

Yes

Answer 6

i think i did that all wrong cause i got the answer 69

Answer 7

did you get 10-7 for the first part and then 20+3 for the second

Answer 8

yeah

Answer 9

Then you should be right, is it not an option?

Answer 10

There is another way to solve the problem

Answer 11

how?

Answer 12

How is it right or how is there another way?

Answer 13

how is there another way?

Answer 14

If you take the two expressions f(x) and g(x) and multiply them together and then plug in -5

Answer 15

How would that look ? like how would i multiply f(x) and g(x) ?

Answer 16

you would write it as (-2x-7)(-4x+3)
Then you would foil to get \[8x ^{2} -6x+28x-21\]
Then combine line terms
\[8x ^{2} +22x-21\]
Then you would plug in -5 for x to get
\[8(5)^{2}+22(-5)-21\]
Then you would get 8(25)+22(-5)-21
And get 200-110-21
Then just simplify that to get the answer

Answer 17

The other way is easier, but either way is a valid method unless a specific method is specified in the directions.

Answer 18

oh okay /.\ you still get 69 but thats none of my answer choices

Answer 19

what are your answer choices?

Answer 20

a. -53 c.3 d. 23

Answer 21

B isnt the answer :P

Answer 22

Well I triple checked it. The answer should be 69. What is this problem from, is it from a school online program or a textbook?

Answer 23

My other question is, is the symbol between the f and g in (f*g)(-5) an open circle or a dot?

Answer 24

an open circle i figured it ment *

Answer 25

if its an open dot what does that mean?

Answer 26

circle*

Answer 27

Oh okay, that does not mean multiplication, that basically means you place the second function, in this case g, inside of f. I will show you if you want.

Answer 28

Yeah :)

Answer 29

Okay it will look like this (-2(-4(-5)+3)-7). I plugged 5 into g(x) and then g(-5) into f(x)

Answer 30

i think i did it wrong cause i got the answer 31

Answer 31

i did it again and got -53

Answer 32

Be careful with symbols.

f*g means f times g.

f o g means f of g.

Answer 33

ok :)

Answer 34

(f o g)(-5) = -53