x^2 -2x +1 =15
(x-1)^2 =15
x=正负根号15+1
x(2x-5)=4x-10
2x^2 -5x-4x+10=0
2x^2 -9x +10=0
(2x-5)(x-2)=0
x=5/2 或 x=2
x^2 +5x +7=3x -11
x^2 +2x +18=0
无解 所以右边应该是 3x+11
x^2 +5x +7 = 3x +11
x^2 +2x -4=0
x^2 +2x +1=5
(x+1)^2 =5
x=正负根号5 -1