We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
0
86
6
avatar

 

I don't understand... How do I find the answer?? I think I need to do Synthetic division but not sure. Please help and show work. Thanks. Sorry

 Feb 21, 2019

Best Answer 

 #2
avatar+18423 
+2

Since you do not know HOW you are supposed to solve this:

   As a follow on to cphill 's answer.....

IF   7x+8   is a factor....then   -8/7 is a root   you can do the synthetic division...or just substitute  -8/7 in to the equation to see if it will make it = zero

7 (-8/7)^3 - 55(-8/7)^2 - 135(-8/7) - 72       DOES = 0   

          so   7x + 8   IS a factor     (this is real easy if you have a calculator with a memory to store (-8/7) and then substitute it in.

 

You can do the same with the second one...... cphill already found   r-8 is NOT a factor.

 Feb 21, 2019
 #1
avatar+101739 
+1

For the first  one...if 7x + 8 is a factor then -8/7 must be a root

 

So.......

 

 

-8/7    [   7       - 55        -135       -72 ]

                        -8            72         72       

             ________________________

              7       -63          -63          0

 

We get a 0 remainder....so   7x + 8 is a factor

 

 

Second one  if r - 8 is a factor,  then  8 is a root

Remember that we need to account for the missing x term in the synthetic division

So we have

 

8 [  7    - 56   0     - 4  ]

              56   0       0

     _______________

       7       0    0     - 4

 

We do not get 0 as a remainder....so....r - 8 is not a factor

 

 

 

cool cool cool

 Feb 21, 2019
 #4
avatar
+1

Sorry for the late reply. Thank you so much. It really helps! I understand it better! smiley

Guest Feb 21, 2019
 #2
avatar+18423 
+2
Best Answer

Since you do not know HOW you are supposed to solve this:

   As a follow on to cphill 's answer.....

IF   7x+8   is a factor....then   -8/7 is a root   you can do the synthetic division...or just substitute  -8/7 in to the equation to see if it will make it = zero

7 (-8/7)^3 - 55(-8/7)^2 - 135(-8/7) - 72       DOES = 0   

          so   7x + 8   IS a factor     (this is real easy if you have a calculator with a memory to store (-8/7) and then substitute it in.

 

You can do the same with the second one...... cphill already found   r-8 is NOT a factor.

ElectricPavlov Feb 21, 2019
 #3
avatar+101739 
0

Yep....I like EP's approach even better!!!!

 

No synthetic division involved !!!!

 

 

cool cool cool

CPhill  Feb 21, 2019
 #5
avatar
0

Thank you for your help! I appreciate it. smiley

Guest Feb 21, 2019
 #6
avatar+101739 
0

No prob.....EP should probably get the "Best Answer"...so...I'll do just that  !!!

 

 

cool cool cool

CPhill  Feb 21, 2019

16 Online Users

avatar
avatar
avatar
avatar