Cross-multiplication password: head × head is the head, tail × tail is the tail, and cross-multiplication adds up to form an item.
For example: x? -4x+3=0
Solution: () () =0
x ╲╱？
x ╱╲？
? x+？ x=-4x
First list this, and then according to the password, the tail × the tail is the tail, and it is concluded that 1×3 is equal to 3.
So x- 1
X. 3
Next, verify another password, cross multiply it and add it as the main item.
Substitute the above into x+3x≦-4x.
Therefore, the change of symbol, because tail × tail =+3, must be positive and negative.
So x- 1
X.-3
Next, verify -x-3x=-4x again.
So (x- 1)(x-3)=0.
X- 1=0 or x-3=0.
X= 1 or x=3.
If the coefficient of the quadratic term is not 1, you can also use this method, but multiply it separately in front.
For example: 2x? -5x- 12=0
Solution: () () =0
This is different from the above. Press the password, and the head is the head, so
x ╲╱？
2x ╱╲？
Other steps are the same as above