1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Tan x-intercepts

  1. Aug 7, 2005 #1
    the tan graph is in the form y=atan(b(x-c))+d how do you determine the "EXACT" x-intercept of this graph in radian form when the d value does not equal 0 and is there a formula for finding the x-intercept when given the equation in the form above using the values of a,b,c and d which control the vertical/horizontal stretch/shift
    Last edited: Aug 7, 2005
  2. jcsd
  3. Aug 7, 2005 #2
    same way you get the zeros for any function: let y=0.
  4. Aug 7, 2005 #3
    whoops i need to edit it i mean as an exact value in radian form like pi/2 for example
  5. Aug 7, 2005 #4
    well, in general, your answer is just going to have to be left in terms of arctangents, multiplied by some factor and then added to by another factor.

    neat answers like pi/2 only come up only in special situations, unfortunately!
  6. Aug 7, 2005 #5
    and my mom is NOT 98! :mad:

  7. Aug 8, 2005 #6
    okay so there are not going to be neat answers so is my only way to get a estimated answer in radian to graph it using a calculator and then trace the zeros? or is there a way to determine it without graphing?
  8. Aug 8, 2005 #7


    User Avatar

    Staff: Mentor

    You need to take the equation

    [tex]\arctan (b (x - c)) + d = 0[/tex]

    and solve it for [itex]x[/itex], that is, rearrange it into the form

    [tex]x = something[/tex]

    Then plug in whatever values you have for [itex]b[/itex], [itex]c[/itex], and [itex]d[/itex]. Where do you get stuck when you try to do this?
  9. Aug 8, 2005 #8
    that wasn't his equation.

    it was a*tan(b(x-c) + d.

    "a" is a stretching/shrinking factor. (i guess it's that there are only two missing letters between atan and arctan and the fact that i mentioned arctan that led you to this.)
  10. Aug 8, 2005 #9
    some simple algebra says: [tex]x=\frac{\tan^{-1}(-\frac{d}{a})}{b}+c[/tex]
    Last edited: Aug 8, 2005
  11. Aug 8, 2005 #10
    "+c," right?
  12. Aug 8, 2005 #11


    User Avatar

    Staff: Mentor

    Oops. I've done too much computer programming in languages that call the arctangent function "atan". :blushing:
  13. Aug 8, 2005 #12
    yea it +c not -c so this gets me the so therefore i can now just like add or substract another period to this answer to get another x-intercept rite?

    thx everyone :smile:
  14. Aug 8, 2005 #13
    yea, oops. maybe i should proofread before i submit
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook