Find the approximated integral value of an equation 1/(x+1) using Simpson's 3/8 rule
a = 0 and b = 1
Interval n = 5Solution:Equation is `f(x)=(1)/(x+1)`
`a=0`
`b=1`
`Delta x =(b-a)/n=(1 - 0)/5=0.2`
The value of table for `x` and `f(x)`
| `x` | `f(x)` |
| `x_0=0` | `f(x_(0))=f(0)=1` |
| `x_1=0.2` | `f(x_(1))=f(0.2)=0.8333` |
| `x_2=0.4` | `f(x_(2))=f(0.4)=0.7143` |
| `x_3=0.6` | `f(x_(3))=f(0.6)=0.625` |
| `x_4=0.8` | `f(x_(4))=f(0.8)=0.5556` |
| `x_5=1` | `f(x_(5))=f(1)=0.5` |
Method-1:Using Simpson's `3/8` Rule
`int f(x) dx=(3Delta x )/8 (f(x_(0))+2(f(x_(3))+f(x_(3))+...+f(x_(n-3)))+3(f(x_(1))+f(x_(2))+f(x_(4))+f(x_(5))+...+f(x_(3))+f(x_(n-1)))+f(x_(n)))`
`int f(x) dx=(3Delta x )/8 [f(x_(0))+3f(x_(1))+3f(x_(2))+2f(x_(3))+3f(x_(4))+f(x_(5))]`
`f(x_(0))=1`
`3f(x_(1))=3*0.8333=2.5`
`3f(x_(2))=3*0.7143=2.1429`
`2f(x_(3))=2*0.625=1.25`
`3f(x_(4))=3*0.5556=1.6667`
`f(x_(5))=0.5`
`int f(x) dx=(3xx0.2)/8 *(1+2.5+2.1429+1.25+1.6667+0.5)`
`=(3xx0.2)/8 *(9.0595)`
`=0.6795`
Solution by Simpson's `3/8` Rule is `0.6795`
Method-2:Using Simpson's `3/8` Rule
`int f(x) dx=(3Delta x )/8 (f(x_(0))+2(f(x_(3))+f(x_(3))+...+f(x_(n-3)))+3(f(x_(1))+f(x_(2))+f(x_(4))+f(x_(5))+...+f(x_(3))+f(x_(n-1)))+f(x_(n)))`
`int f(x) dx=(3Delta x )/8 [(f(x_(0))+f(x_(5)))+2(f(x_(3)))+3(f(x_(1))+f(x_(2))+f(x_(4)))]`
`=(3xx0.2)/8 [(1 +0.5)+2xx(0.625)+3xx(0.8333+0.7143+0.5556)]`
`=(3xx0.2)/8 [(1 +0.5)+2xx(0.625)+3xx(2.1032)]`
`=(3xx0.2)/8 [(1.5)+(1.25)+(6.3095)]`
`=0.6795`
Solution by Simpson's `3/8` Rule is `0.6795`
This material is intended as a summary. Use your textbook for detail explanation.
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