How do i calculate are on Trapezoidal rule?

I have to calculate are on using Trapezoidal rule, how do i do it? f(x) = 11*sin(0.5*x)-3*x; [1,4] a = 1; b = 4; n = 7; And the answer have to be second (on the left) trapezoidal area with 2 decimal places. n = is the interval points

Answer 1

[Torsten]

n is the number of trapezoids or the number of interval points ?

Best wishes

Torsten.

Answer 2

[markus palmu]

The n is interval points

Thanks by markus

[Torsten]

So the second trapezoid goes from x1=1.5 to x2=2.

The parallel sides have lengths

l1=f(1.5)=11*sin(0.5*1.5)-3*1.5 and

l2=11*sin(0.5*2)-3*2.

So the area of this trapezoid is

A=(x2-x1)*(l1+l2)/2=0.5*((11*sin(0.5*1.5)-3*1.5)+(11*sin(0.5*2)-3*2))/2.

Best wishes

Torsten.

[markus palmu]

it is not right answer :(

[Torsten]

I get A=1.56 from the above formula.

If you use your electronic calculator, maybe you have to switch from degrees to radians in the sin-function :-)

Best wishes

Torsten.