1) x^2-10x+25+x^2+8x+16=2x^2
2x = 41
x = 20,5
2) 5x^2-12x+7=0
D= 144 - 140 = 4
x1,2 = (12+-2)/10
x1 = 1,4 x2 = 1
3) x^2-121=0
x^2=121
x1 = 11
x2 = -11
4) 5x^2+20x=0
5x(x+4)=0
x=0 или x= 4
5) (x-2)(-x-1)=0
x=2 или x= -1
вроде так
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Answers & Comments
1) x^2-10x+25+x^2+8x+16=2x^2
2x = 41
x = 20,5
2) 5x^2-12x+7=0
D= 144 - 140 = 4
x1,2 = (12+-2)/10
x1 = 1,4 x2 = 1
3) x^2-121=0
x^2=121
x1 = 11
x2 = -11
4) 5x^2+20x=0
5x(x+4)=0
x=0 или x= 4
5) (x-2)(-x-1)=0
x=2 или x= -1
вроде так