The solution is 3 and the extraneous solution is -1.
What is the modulus function?
The modulus function is the function which gives the magnitude or absolute of the number in the variable.
|x|=x if x>0
-x if x<0
0 if x=0
So according to question,
|7x+21|=14x
case-1: if 7x+21>0
⇒7x>-21
⇒x>-21/7
⇒x>-3
if 7x+21>0 , Using the modulus function property
|7x+21|=14x
⇒7x+21=14x
⇒14x-7x=21
⇒7x=21
⇒x=21/7
⇒x=3 which is also x>-3
x=3 is the solution
case-2: if 7x+21<0
⇒7x<-21
⇒x<-21/7
⇒x<-3
if 7x+21<0 , Using the modulus function property
|7x+21|=14x
⇒-(7x+21)=14x
⇒-7x-21=14x
⇒14x+7x=-21
⇒21x=-21
⇒x=-21/21
⇒x=-1 for which x<-3 is not true
x=-1 is an extraneous solution.
Therefore the solution is 3 and the extraneous solution is -1.
Learn more about the modulus function
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