M1v1=m1v1'+'(!)
(M1v1²)/2=(m1v1'²)/2+(m2v2'²)
M1v1-m1v1'=m2v2'
M1v1²-m1v1'²=m2v2'²
V1+v1'=v2'(!!)
V2'=(m1v1-m1v1')/m2
M2v1+m2v1'=m1v1-m1v1'
V1'(m1+m2)=v1(m1-v2)
v1'=v1(m1-m2)/(m1+m2)
v1'=(2*4)/8=1m/c
M1v1=m1v1'+'(!)
(M1v1²)/2=(m1v1'²)/2+(m2v2'²)
M1v1-m1v1'=m2v2'
M1v1²-m1v1'²=m2v2'²
V1+v1'=v2'(!!)
V2'=(m1v1-m1v1')/m2
M2v1+m2v1'=m1v1-m1v1'
V1'(m1+m2)=v1(m1-v2)
v1'=v1(m1-m2)/(m1+m2)
v1'=(2*4)/8=1m/c