 Kobrasmary 
                                                08.02.2021 18:14
                                                
                                                Kobrasmary 
                                                08.02.2021 18:14
                                             alenkaabramovic 
                                                08.02.2021 18:15
                                                
                                                alenkaabramovic 
                                                08.02.2021 18:15
                                             Balans456 
                                                31.05.2019 08:10
                                                
                                                Balans456 
                                                31.05.2019 08:10
                                             tanya596 
                                                31.05.2019 08:10
                                                
                                                tanya596 
                                                31.05.2019 08:10
                                             golubtsovanyut 
                                                06.05.2021 08:55
                                                
                                                golubtsovanyut 
                                                06.05.2021 08:55
                                             davvechannel 
                                                06.05.2021 08:55
                                                
                                                davvechannel 
                                                06.05.2021 08:55
                                             encl3 
                                                06.05.2021 08:55
                                                
                                                encl3 
                                                06.05.2021 08:55
                                            
↑AB = ↑DC =↑ b
↑BC = ↑AD = ↑ a
↑AM = ↑AB + 3/4 ↑ BC = ↑ AB + 3/4 ↑AD = ↑b +3/4 ↑a
↑MD=-↑AM +↑AD = -(↑b +3/4 ↑a) +a = 1/4↑a -↑b
или
↑MD=↑MC +↑CD=↑MC -↑DC =1/4↑a -↑b