The standard form of a quadratic polynomial is ax2+bx+c ,
where a is the coefficient of x2,
b is the coefficient of x
and c is called the constant term.
We know that
(x+a)(x+b)=x2+(a+b)x+ab
Using this identity we have,
⇒(x+1)(x+2)=x2+3x+2,
thus coefficient of x is 3.
⇒(x−1)(x−2)=x2−3x+2,
thus coefficient of x is -3.
⇒(x−1)(x+2)=x2+x−2,
thus coefficient of x is 1.
⇒(x+1)(x−2)=x2−x−2,
thus coefficient of x is -1.