When an object moves in a straight line with uniform speed change, the displacement in the third second is 15 m, the displacement in the eighth second is 5 m, and the acceleration is - 2 m per square second I solved 19 meters per second, but the answer was 20 meters per second. I used the calculator to verify it countless times. I don't know what's wrong PS: the acceleration is added after I calculate it. If you have any questions, you can calculate the acceleration according to the conditions

When an object moves in a straight line with uniform speed change, the displacement in the third second is 15 m, the displacement in the eighth second is 5 m, and the acceleration is - 2 m per square second I solved 19 meters per second, but the answer was 20 meters per second. I used the calculator to verify it countless times. I don't know what's wrong PS: the acceleration is added after I calculate it. If you have any questions, you can calculate the acceleration according to the conditions

a=(15-5)/(8-3)=2m/s^2
Vo=15+a/2+(3-1)*a=15+1+2*2=20m/s
supplement
There is something wrong with your checking method
You use the wrong way to find the answer, and then check the same way, countless times not wrong ah