28-25+12=2x-16x-6x+20x
15=0*x
0 не равно 15. решений нет
X +81/x =18
(x² +81)/x =18
x² +81 =18x
x² -18x +81 =0
D =18² -4*81 =0
x1,x2 =(18+-0)/2 =9
1) (a-b)(a+b)=a²-b²
2) (a-2)(a+2)=a²-4
3) (1-b)(1+b)=1-b²
4) (3a-b)(3a+b)=9a²-b²
5) (3x-1)(3x+1)=9x²-1
6)(13m-11n)(13m+11n)=169m²-121n²
7) (10p+7q)(7q-10p)=49q²-100p²
8) (4-5y)(5y+4)=16-25у²
9) (a+2)²=а²+4а+4
10) (3b-1)²=9b²-6b+1
11) (x-8)²=x²-16x+64
<span>12) (1+4y)</span>²=1+8y+16y²
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