Help me with creating a rational function with vertical asymptotes

Bruce Partridge

Bruce Partridge

Answered question

2022-02-16

Help me with creating a rational function with vertical asymptotes x=±1 and oblique asymptote of y=2x3 and a y-intercept of 4.

Answer & Explanation

vazen2bl

vazen2bl

Beginner2022-02-17Added 9 answers

First, you want your function to have vertical asymptotes at x=1,-1. So we really want
1(1x)(1+x)    (1) Now, as x; this has a "oblique" asymptote of 0, so we can just add the asymptote we want:
1(1x)(1+x)+2x3
Now, lets
jorgegalar0xk

jorgegalar0xk

Beginner2022-02-18Added 5 answers

For one family of rational functions f(x) having vertical asymptotes only at x=±1, consider those that can be written in the form
f(x)=p1(x)+p2(x)(x+1)m+p3(x)(x1)n
for some positive integers m,n, and some polynomials p1,p2,p3, with p2,p3 in particular being non-0 polynomials of respective degrees<m,<n. Such a function has a slant asymptote if and only if P1(x) is the line toward which the function tends asymptotically.
Hence, any rational functions f(x) in our family having y=2x-3 for a slant asymptotes can be written in the form
f(x)=2x3+p2(x)(x+1)m+p3(x)(x1)n,
with m,n,p2,p3, as described above.
We're just looking for one such example, so to make it simpler on ourselves, we may as well assume m=n=1, so that p2,p3, must be constant polynomials, and our function will be
f(x)=2x3+Ax+1+Bx1
for some non-zero constants A,B. All that remains is to choose non-zero constants A,B so that f(0)=4 (i.e.: f(x) has y-intercept 4).

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