Question

直接开平方解方程 （2x-1)²=5和x²+6x+9=4.

还有（15+x)²=300

Answer 1

1. （2x-1)²=5

   2x-1=±√5

   2x=±√5+1

   x=2/√5+1 或 x=2/-√5+1

2. x²+6x+9=4

   （x+3）²=4

   x+3=±√4

   x+3=±2

   x=2-3=-1或

   x=-2-3=-5

Answer 2

1. 2x - 1 = sqrt(5) or 2x - 1 = -sqrt(5)

   so x1 = (1 + sqrt(5))/2, x2 = (1 - sqrt()5)/2

2. x^2 + 6x + 9 = (x + 3)^2 = 4

       so (x + 3) = 2 or (x + 3) = -2

       so x1 = -1, x2 = -5

3. (15 + x)^2 = 300

   so 15 + x = sqrt(300) or 15 + x = -sqrt(300)

   so x1 = -15 + sqrt(300), x2 = -15 - sqrt(300)

Answer 3

(2x-1)²=5
解：2x-1=±√5
∴x=1+5√或 1-√5
x²+6x+9=4
解：(x+3)²=4
x+3=±2
∴x= -5或 -1

Answer 4

x=二分之√5-1 x=√4-3 x=√300-15