SOLUTION: If f(x)=4-5x and g(x)=-x²+2x‚ find (f+g)(-1)

Algebra ->  Rational-functions -> SOLUTION: If f(x)=4-5x and g(x)=-x²+2x‚ find (f+g)(-1)      Log On


   

Question 1205293: If f(x)=4-5x and g(x)=-x²+2x‚ find (f+g)(-1)
Found 2 solutions by ikleyn, math_tutor2020:
Answer by ikleyn(52914) About Me  (Show Source):
You can put this solution on YOUR website!
.

Find  f(-1)  and g(-1)  separately and then add these values.

Doing it is very easy - so, I leave this exercise to you to complete.


Saying "very easy", I mean that these calculations are at the complexity level of the multiplication table,
so I hesitate to go to further explanations.



Answer by math_tutor2020(3817) About Me  (Show Source):
You can put this solution on YOUR website!

Answer: 6


I'll show two methods.
Method 1
(f + g)(x) = f(x) + g(x)
(f + g)(x) = (4-5x) + (-x^2+2x)
(f + g)(x) = -x^2 - 3x + 4
(f + g)(-1) = -(-1)^2 - 3(-1) + 4
(f + g)(-1) = -1 - 3(-1) + 4
(f + g)(-1) = -1 + 3 + 4
(f + g)(-1) = 6


Method 2
f(x) = 4 - 5x
f(-1) = 4 - 5(-1)
f(-1) = 4 + 5
f(-1) = 9
g(x) = -x^2+2x
g(-1) = -(-1)^2+2(-1)
g(-1) = -1+2(-1)
g(-1) = -1-2
g(-1) = -3
(f + g)(-1) = f(-1) + g(-1)
(f + g)(-1) = 9 + (-3)
(f + g)(-1) = 9 - 3
(f + g)(-1) = 6


There are many online tools you can use to verify the answer.
In Desmos you can type the functions in as given.
Make sure to type x^2 to mean x%5E2
Once functions f(x) and g(x) are set up, you can then have Desmos compute f(-1)+g(-1)
https://www.desmos.com/calculator/fn0hcid0bq
Refer to the calculations in the left-side panel.
I recommend using Desmos as a way to verify the answer, rather than do all of your homework for you.
GeoGebra is another similar and very useful tool that you could use.