# Really need help with these questions

• Feb 3rd 2010, 11:50 AM
Notsogoodatmaths
Really need help with these questions
1.I need to evaluate (x+x^3)dx with limits 2 and 1

ii. estimate the above integral using the trapezium rule using 5 strips

2.i need to use the trapezium rule with 4 strips to estimate root(1+x^2) with limits of 4 and 0

3.the gradient function is dy/dx= 1/x^2 - xrootx

4.I need to find the stationary point of the graph y= (1/x) + (1/x^2) - (1/x^3) and need to determine their natures of each

I need help with these 4 please. Dont think you have to answer them all, but i do need all the answers and working out Thanks

Need replies ASAP
• Feb 3rd 2010, 02:15 PM
TKHunny
Well, do it, Good Fellow.

Given f(x) = x + x^3 and 5 strips, you will need:

f(1)
f(1.2)
f(1.4)
f(1.6)
f(1.8)
f(2)

Let's see what you get.
• Feb 3rd 2010, 02:51 PM
Notsogoodatmaths
(Headbang)thats the thing i dont have a clue and need to know if i want to keep my head
• Feb 3rd 2010, 03:12 PM
Notsogoodatmaths
ive done the bit in the table but now need to apply the rule. help?
• Feb 3rd 2010, 07:41 PM
TKHunny
You'll never get it with a screen name like that.

1.2 - 1.0 = 0.2
1.4 - 1.2 = 0.2
1.6 - 1.4 = 0.2
1.8 - 1.6 = 0.2
2.0 - 1.8 = 0.2

This makes it appears as though the interval width is 0.2.

Now build the little trapezoids.

Here's the first one.
0.2*(f(1.0)+f(1.2))/2

Let's see what you get for the rest.