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8y-3-y-7=4
7y=7
y=1
tgx = 19
tg2x = 2tgx/(1 - tg²x)
tg2x = 2 · 19/(1 - 361) = - 38/360 = -19/180
1
x-2y=4⇒x=2y+4
xy=6
2y²+4y-6=0
y²+2y-3=0
y1+y2=-2 U y1*y2=-3
y1=-3⇒x1=-6+4=-2
y2=1⇒x2=2+4=6
(-2;-3);(6;1)
2
x²-y²=72⇒(x-y)(x+y)=72⇒x-y=72:9=8
x+y=9
прибавим
2x=17
x=8,5
8,5+y=9
y=0,5
(8,5;0,5)