<span>1) 3a(a+2)-(a+3)²= 3a(a+2)-(a+3)(a+3)=3a²+6a-(a²+6a+9)=2a²-9</span>
<span><span>2) 3(y-1)²+6y = 3(y-1)(y-1)+6y=3(y²-2y+1)+6y=3y²-6y+3+6y=3y²+3=3(y²+1)</span></span>
<span><span><span>3) 8c+4(1-c)² = 8c+4(1-2c+c²)=8c+4-8c+4c²=4(c²+1)</span></span></span>
<span><span><span><span>4) 4ab+2(a-b)</span>² = 4ab+2(a²-2ab+b²)=4ab+2a²-4ab+2b²=2(a²+b²)</span></span></span>
<span><span><span><span>5) 3(x+y)²-6xy = 3(x²+2xy+y²)-6xy=3x²+6xy+3y²-6xy=3(x²+y²)</span></span></span></span>
100\%-35\%=65\% от цены.
2120:100*65=1378 (рублей стоит платье со скидкой)
3x²+2y²=50|*4⇒12x²+8y²=200
12x²+8y²=50x
Отнимем
200-50x=0
50x=200
x=200:50=4
3*16+2y²=50
2y²=50-48=2
y²=2:2=1
y=+-1
(4;-1) ;(4;1)