Why did I get different results by using degree/radiance as the unit in the integration?

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Shuangfeng Jiang
Shuangfeng Jiang 2020-6-23
评论： KSSV 2020-6-23
today I wonder if the unit (degree/radiance) of integration variable matters in Matlab, so I tried these 2 peices of codes:
x_tst=0:0.1:180; % in degree
y_tst=sind(x_tst);
Q1=trapz(x_tst,y_tst)
Q1 =
1.145915299373423e+02
x_tst_deg=0:0.1:180;
x_tst_rad=x_tst_deg./180.*pi;% in radiance
y_tst=sin(x_tst_rad);
Q2=trapz(x_tst_rad,y_tst)
Q2 =
1.999949230172279
As you can see, the results are different, could someone tell me why we have this problem in MATLAB?
Must we use radiance as the unit of angle in Matlab (especially in the integration)?
What if I would like to adopt 'degree' as the unit of the integration variable?

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KSSV
KSSV 2020-6-23
编辑：KSSV 2020-6-23
Note that both the results are same...but they are in different units....
Your Q1 is in degrees and Q2 is in radians.....Convert them to the same units and see...
% Check in degrees
Q2*180/pi
Q1
% check in radians
Q1*pi/180
Q2
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KSSV
KSSV 2020-6-23
Simple man...your x-values i.e x_tst are in radians for Q1 and are in degrees for Q2...as the area is length*breadth...your x-values are different in both the cases...so your values are different.

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