5х + 4 = 3х – 8
5х – 3х = – 8 – 4
2х = – 12
х = – 12 : 2
х = –6
(cos²t-ctg²t)/(sin²t-tg²t)=(cos²t-cos²t/sin²t)/(sin²t-sin²t/cos²t)=
=(cos²t·sin²t-cos²t)·cos²t/sin²t(cos²tsin²t-sin²t)=
=cos⁴t(sin²t-1)/sin⁴t(cos²t-1)=cos⁴t·(-cos²t)/sin⁴t·(-sin²t)=cos⁶t/sin⁶t=ctg⁶t;
5,06-0,24=4,82дм(4дм,8см,2мм)