SOLUTION: 5^(2x+1) + 25 = 5^(x+3) + 5^x

Algebra ->  Exponents -> SOLUTION: 5^(2x+1) + 25 = 5^(x+3) + 5^x      Log On


   



Question 1094771: 5^(2x+1) + 25 = 5^(x+3) + 5^x
Found 2 solutions by ikleyn, MathTherapy:
Answer by ikleyn(52794) About Me  (Show Source):
You can put this solution on YOUR website!
.
Your equation is

5%2A5%5E%282x%29+%2B+25 = 125%2A5%5Ex+%2B+5%5Ex,   or, which is the same,

5%2A5%5E%282x%29+-+126%2A5%5Ex+%2B+25 = 0.


Introduce new variable  u = 5%5Ex.  Then your equation will take the form

5u%5E2+-+126u+%2B+25 = 0.

Apply the quadratic formula to find the solutions for u:


u%5B1%2C2%5D = %28126+%2B-+sqrt%28126%5E2+-4%2A5%2A25%29%29%2F%282%2A5%29 = %28126+%2B-+124%29%2F10.

u%5B1%5D = %28126%2B124%29%2F10 = 25;

u%5B1%5D = %28126-124%29%2F10 = 1%2F5.


From u%5B1%5D = 25 = 5%5Ex you get the solution for x: x= 2.

From u%5B2%5D = 1%2F5 = 5%5Ex you get another solution for x: x= -1.


Answer.  The original equation has two solutions:  x = 2  and  x = -1.

The method of introducing new variable I showed you in this solution, is the standard method for problems like this.


To see more examples of problems solved in this way, see the lesson
    - Solving exponential equations
in this site.



Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!
5^(2x+1) + 25 = 5^(x+3) + 5^x
5%5E%282x+%2B+1%29+%2B+25+=+5%5E%28x+%2B+3%29+%2B+5%5Ex+
5%5E%282x+%2B+1%29+-+5%5E%28x+%2B+3%29+-+5%5Ex+%2B+25+=+0
%285%5E%282x%29+%2A+5%5E1%29+-+%285%5Ex+%2A+5%5E3%29+-+5%5Ex+%2B+25+=+0
%285%5Ex+%2A+5%5Ex+%2A+5%5E1%29+-+%285%5Ex+%2A+5%5E3%29+-+5%5Ex+%2B+25+=+0
(a * a * 5) – (a * 125) – a + 25 = 0 -------- Substituting matrix%281%2C3%2C+a%2C+for%2C+5%5Ex%29
5a%5E2+-+125a+-+a+%2B+25+=+0
5a(a - 25) - 1(a - 25) = 0
(5a – 1)(a – 25) = 0
5a – 1 = 0	OR 		a – 25 = 0 
5a = 1		OR		a = 0 + 25 
matrix%281%2C3%2C+a%2C+%22=%22%2C+1%2F5%29		OR		a = 25

matrix%281%2C5%2C+a%2C+%22=%22%2C+1%2F5%2C+%22=%22%2C+5%5Ex%29   	    OR 	      matrix%281%2C5%2C+a%2C+%22=%22%2C+25%2C+%22=%22%2C+5%5Ex%29
matrix%281%2C3%2C+5%5Ex%2C+%22=%22%2C+1%2F5%29	    OR	      matrix%281%2C3%2C+5%5Ex%2C+%22=%22%2C+25%29
matrix%281%2C3%2C+5%5Ex%2C+%22=%22%2C+5%5E%28-+1%29%29	    OR        matrix%281%2C3%2C+5%5Ex%2C+%22=%22%2C+5%5E2%29