Ответ 0
cos a-sin a *(cos a /sin a)=cos a -cos a=0
!!!!!!!!!!!!!!!!!!!!!!!!!
1)
(38²-28²): (47²-19²)=(38-28)(38+28) : (47-19)(47+19)=10*66 / 28*66 =10/28=5/24
2)
(53²-25²) : (79²-51²)=(53-25)(53+25) : (79-51)(79+51)=28*78/28*130=39/65
3)
(181²-61²) : (219²-77²)= (181-61)(181+61) : (219-77)(219+77)=120*242/142*296=
=15*121/71*37=1815/2627
4)
(200²-380²) : (420²-160²)= (200-380)(200+380) : (420-160)(420+160)= -180*580/260*580=-18/26=-9/13
√3*12 / √2*2*25 = √36/√100 = 6/10 = 0.6
1/7х^2*7х^3
сокращаем
х^2 х^3
ответ: х^5