Pre-Calc

Can someone show me how to do this please. I am stuck.


find a number x such that
e^2x – 12e^x =13

  1. 👍 0
  2. 👎 0
  3. 👁 112
asked by Roy
  1. Substitute y=e^x to get a quadratic equation:
    y²-12x+13=0
    Solve for y.
    Substitute the values of y=e^x into the original equation to make sure that all the roots are feasible/defined.
    See also previous example:
    http://www.jiskha.com/display.cgi?id=1291874924

    1. 👍 0
    2. 👎 0
    posted by MathMate
  2. let e^x = t
    then
    e^2x – 12e^x =13 becomes
    t^2 - 12t - 13 = 0
    (t-13)(t+1) = 0
    t = 13 or t = -1

    then e^x = 13 or e^x = -1
    x = ln 13 or x = ln(-1)
    but in ln(a) a > 0

    so x = ln 13

    1. 👍 0
    2. 👎 0
    posted by Reiny
  3. I slipped in the sign of the transformed equation. Instead of
    y²-12x+13=0
    it should read
    y²-12x-13=0

    Go with Reiny's solution.

    1. 👍 0
    2. 👎 0
    posted by MathMate
  4. Thank u both

    1. 👍 0
    2. 👎 0
    posted by Roy

Respond to this Question

First Name

Your Response

Similar Questions

  1. math percents

    Can you check these? 18% of 90 is what number? i got 16.2 what number is 41% of 800? i got: 1951.22 what number 5% of 522? i got : 10440 70% of 279 is what number? i got: 195.3 what number is 90% of 13? i got : 14.44 9% of 351 is

    asked by marko on March 1, 2012
  2. Math mrs sue

    Can you check these? 18% of 90 is what number? i got 16.2 what number is 41% of 800? i got: 1951.22 what number 5% of 522? i got : 10440 70% of 279 is what number? i got: 195.3 what number is 90% of 13? i got : 14.44 9% of 351 is

    asked by Marko on March 1, 2012
  3. 5th

    find the missing number: 18,20,20,24,27,27,____,30,33,34,36,36,_ I need you to show me this answer cause, i got stuck with this one. thank you!

    asked by pat on September 29, 2010
  4. Algebra

    I have 3 questions I'm stuck on and would love for someone to explain and show me how to solve them so I can also solve the other one. Find the partial sum S6 1. An=3n+2 2. Find the number of terms n in an arithmetic sequence if

    asked by Jess on April 3, 2013
  5. math help please

    An art teacher had a total of t markers. He gave an equal number of markers to each of 18 students and had 16 markers left over. Which equation could be used to find n , the number of markers each student received? A t = 18n B t =

    asked by math on April 27, 2016
  6. math

    the units of a number is 4 more than the tens digit. If the digits are reversed the new number is 1 less than twice the original number. Use a system of equations and substitution to find the number. I'm stuck?!?!

    asked by Rachel on March 1, 2016
  7. lab

    Number of moles of oxygen gas produced from the complete catalyzed decomposition of 6.80ml sample of a 3.5% solution. Density of the 3.5% solution of H2O2 is 1.01g/ml Let's find out what you know about this and work from there.

    asked by Melba on September 25, 2006
  8. English- A Raisin in the Sun

    I'm stuck on these in A Raisin in the Sun: Why does Mama decide not to move? In what way does she show herself to be stronger than her children? I'm stuck, please help!

    asked by Anonymous on September 1, 2007
  9. Math help plz

    How thick is a pile of paper? Find a relationship between the number of folds and the number of layers. Note your observations. Number of folds Number of layers 0 1 1 2 2 4 3 8 4 14 5 23 Plz help im so stuck on this question Are

    asked by Jessie on October 15, 2006
  10. Math

    Hello. I'm not asking for you to give me the answer to this question, but could you please help me? Hallie is trying to win the grand prize on a game show. Should she try her luck by spinning a wheel with 6 equal sections labeled

    asked by TreatPPLHowUWant2BTreated on March 5, 2019

More Similar Questions