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

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

    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

    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.

    posted by MathMate
  4. Thank u both

    posted by Roy

Respond to this Question

First Name

Your Answer

Similar Questions

  1. Pre-Calc

    I'm stuck on a pre-calc problem. I need to find y as a function of x, where the constant c is a positive number for In(y-1)+In(y+1)= -x+c express your question as ln[(y-1)(y+1)] = -x+c change that to exponential form e^(-x+c) =
  2. algebra

    find the LCM of 15ef and 12e^4 (12e to the power of 4) Please show the steps. I do not understand how to do this.
  3. Pre-Calc

    Can you show me how to find the rectangular equation of r=2costheta + 3 sin theta All I need is an example to work off I was absent today from Pre-Calc and I have homework to do and no explanation with them-Please help with this
  4. Pre-Calc

    I'm so stuck-this stuff is so far above me right now-Please help (3x^3-5^2+6x-9)/(x+5) or can someone direct me to a site that can solve this and show the steps-I don't even know where to start Thank you
  5. Pre-Calc

    Please help stuck on this one question Find (fog)(2) and (f+g)(2) when f(x)= 1/x and g(x)=4x+9
  6. Pre-Calc

    I'm so stuck-this stuff is so far above me right now-Please help where do I even start? Any hint would be so helpful- (3x^3-5^2+6x-9)/(x+5) or can someone direct me to a site that can solve this and show the steps-I don't even
  7. Pre-Calc

    I am stuck solving this problem, any help please..Many thanks find all numbers x that satisfy the given equation ln(2x) ------- =2 ln(3x)
  8. Pre Calc

    use properties of the trigonometric function to find the exact value of each expression. Do no use a calculator. sec ( - pi/18) * cos (37 pi)/18 I do not see how to do this problem. Every time I do it out I get a reference angle
  9. Pre-Calculus

    Can you show me how to find the rectangular equation: r=2cos(theta) + 3 sin (theta) All I need is an example to work off I was absent today from Pre-Calc and I have homework to do and no explanation with them-Please help with this
  10. Pre-Calc

    Hello! I'm stuck on how to do this problem and would appreciate some help! Choose a non-zero complex number c for f(z) = z2+ c. Find a complex number v that is in the escape set. Find a complex number w that is in the prisoner

More Similar Questions