1)= -sin²a-tga-cosa*sina
2)= cosa*sina+ sin²a
3)= (-cosa*sina-sin²a)/(cos²a-sin²a)= (-sina)/cosa-sina
4x-y=11
6x-2y=13
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y=4x-11
6x-2(4x-11)=13
6x-8x+22=13
-2x=13-22
-2x=-9, x=9/2, x=4,5
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y=4.4,5-11, y=18-11,y=7
/x,y/=/4,5, 7/
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5x+3y=4
2x-y=-5\*3
5x+3y=4
6x-3y=-15
11x=11
x=1
найдем y:
2*1-y=-5
2-y=-5
-y=-3\*(-1)
y=3
ответ(1;3)