17.
3(x-y)²=3(x²-2xy+y²)=3x²+3y<span>²-6xy
</span>
18.
a²+(3a-b)²=a²+9a²-6ab+b²=10a²+b<span>²-6ab
19.
(a-4)</span>²+a(a+8)=a²-8a+16+a²+8a=2a<span>²+16
20.
(a-c)(a+c)-(a-2c)</span>²=a²-c²-a²+4ac-4c²=4ac-5c<span>²</span>
11х - 3 = 17 - 6х
11х + 6х = 17 + 3
17х = 20
х = 20/17
Л.ч. 11×20/17 - 3 = 220/17 - 3 = 220/17 - 51/17 = 169/17
П.ч. 17 - 120/17 = 289/17 - 120/17 = 169/17
Ответ: {20/17}
4х-9=0
4х=9
х=9/4
x= 2, 1/4( 2 целых одна четвертая или 2.25)
Вот......................