cos2t - sin2t/tg(-t)*ctgt=cos2t-sin2t/-tgt*ctgt=cos2t-sint/-1=cos2t+sin2t=1
tg(-t)=-tgt
-tgt*ctgt=-sint/cost*cost/sint=-1
cos2t+sin2t=1
{3y+x=5
{13y-2x=11
{x+3y=5|*2
{-2x+13y=11
+{2x+6y=10
+{-2x+13y=11
19y=21:19
y=21/19
21/19*3+x=5
x=5-63/19
x=5-3 6/19
x=1 13/19
{7x+5y=17|*3
{8x-3y=5|*5
+{21x+15y=51
+{40x-15y=25
61x=76:61
x=76/61
76/61*7+5y=17
5y=17-553/61
5y=17-9 4/61
5y=7 57/61:5
y=96,8
2(5x+3)-1 > 7x-2
10x+6-1 > 7x-2
10x-7x > -2-5
3x > -7
x > -7/3
x > -2 ¹/₃
--------- -2 ¹/₃ -------------------
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x∈(-2 ¹/₃; +∞)