How to calculate the area of specific path under the curve?

this is the area i want to calculate

the code i used

>> i=[0:0.5:3.5];

>> l=18*sqrt(i);

>> plot (i,l)

>> grid on

>>

Answer 1

[KSSV]

Read about trapz.

[Salah Alfiky]

just tell me the code

[Louis Alexander]

like this:

i=[0:0.5:3.5];
l=18*sqrt(i);
plot (i,l)
grid on
Q = cumtrapz(l,i)
Q = trapz(l,i)

Answer 2

[Louis Alexander]

if your curve can be expressed as a function, you can choose

 integral、integral2 or integral3