Question

Describe the steps you would take to sketch the graph p(x)=2x^(3)+7x^(2)-3x-18

Answer 1

Answer:

When we have a given function, y = f(x), the general way of graphing the function is finding a lot of coordinate pairs (x, f(x)) and graphing them in a coordinate axis, and then connect them.

So here we have:

p(x) = 2x^(3)+7x^(2)-3x-18

Just let's find the value of p(x) for different values of x, and let's do it.

p(0) = 2*0^(3)+7*0^(2)-3*0-18 = -18

Then the point (0, -18) belongs to the graph

p(1) = 2*1^(3)+7*1^(2)-3*1-18 = 2 + 7 - 3 - 18 = -12

then the point (1, - 12) belongs to the graph.

p(-1) =  2*(-1)^(3)+7*(-1)^(2)-3*(-1)-18  = -2 + 7 + 3 - 18 = -10

then the point (-1, -10) belongs to the graph:

p(2) =  2*2^(3)+7*2^(2)-3*2-18 = 16 + 28 - 6 - 18 =  20

Then the point (2, 20) belongs to the graph

p(-2) =  2*(-2)^(3)+7*(-2)^(2)-3*(-2)-18 = -16 + 28 + 6 - 18 = 0

Then the point (-2, 0) belongs to the graph.

p(-3) =  2*(-3)^(3)+7*(-3)^(2)-3*(-3)-18 = -54 + 63 + 9 - 18 = 0

Then the point (-3, 0) belongs to the graph.

Now that we have 6 points we can graph them and try to connect them.

We also know that this is a cubic polynomial, so we can expect that it changes its direction two times (no more than that) then knowing that we can estimate a shape for the graph, and you will obtain something like the graph of the image below, where I just connected the known points.