The left extension is ab-a-b+ 1.

2.

The matching method is to use the formula A 2+2AB+B 2 = (A+B) 2.

a^2-2ab+b^2=(a-b)^2

In the equation, the unknown quantity is represented on the left in the form of polynomial square, and the constant and fixed value are represented on the right. Then open a root sign to solve it.

For example:

x^2-2x=0

x^2-2x+ 1= 1

(x- 1)^2= 1

Root symbol:

X- 1= 1 or x- 1=- 1.

X=2 or x=0.

3.

Root symbol:

A-b=√ 1 1 or a-b =-√1.

The formula used is: A 2 = B A = B

4.

Vieta theorem:

Let the two real roots of the equation aX 2+bx+c = 0 (a ≠ 0) be X 1 and x 2, respectively, then there are

x 1+x2=-b/a

x 1x2=c/a

Vieta's theorem can be deduced as follows:

Let the equation have two real roots x 1 and x2, then both x 1 and x2 satisfy the equation.

ax 1^2+bx 1+c=0( 1)

ax2^2+bx2+c=0 (2)

( 1)-(2)

a(x 1^2-x2^2)+b(x 1-x2)=0

a(x 1+x2)(x 1-x2)+b(x 1-x2)= 0

(x 1-x2)[a(x 1+x2)+b]= 0

x 1=x2，x 1=x2=-b/2a

x 1+x2=-b/a

x 1≠x2 x 1+x2=-b/a

Similarly, you can deduce x 1x2=c/a by yourself.