# Use graph sketching techniques to graph: y= (x-2)(x+3)(x+5) Use graph sketching techniques to graph: y= (x-2)(x+3)(x+5)

*print*Print*list*Cite

### 1 Answer

To graph polynomials we know that there are no asymptotes (since polynomials are very well-behaved) so we just need to use the remaining graphing techniques.

(1) **Intercepts.** The function is in factored form, so the x-intercepts are found when y=0, which is at x=2, x=-3 and x=-5. The y-intercept is at x=0 which is at `y=(-2)(3)(5)=-30`.

(2) **Extrema.** Expanding out the polynomial gives `y=x^3+6x^2-x-30`. The derivative is now easy to find using the power rule. `y'=3x^2+12x-1`. Using the quadratic formula, the zeros are at `x=-2+-sqrt{39}/3 approx 0.08, -4.08`. The second derivative is `y''=6x+12=6(x+2)`. This means from the second derivative test that the root at `x approx 0.08` is a local minimum and the root at `x approx -4.08` is a local maximum.

(3) **Inflection Points.** The inflection point is found from the zero of the second derivative, which is at x=-2. Since this is a simple root, the second derivative changes sign on either side of the inflection point, so it goes from concave down to concave up.

(4) **Infinity.** Since this is a polynomial, we can tell that as x goes to the right, the function goes up, and as x goes to the left, the function goes down. This is the behaviour of the leading term `x^3`.

Putting this together we get the graph: