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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

Guest Feb 21, 2019

#2**+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.

ElectricPavlov Feb 21, 2019

#1**+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

CPhill Feb 21, 2019

#2**+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