One-dimensional Quadratic Equation in Grade Three: Students are going to hold a photo exhibition, and the photos are each rectangular paper with a length of 18cm and a width of 12cm.

One-dimensional Quadratic Equation in Grade Three: Students' Union is going to hold a photography exhibition, and a circle of colored paper with the same width is set around the rectangular paper photos of 18cm and 12cm in each Zhang Changkuan. After testing, it is more beautiful when the area of colored paper is 2/3 of the photo area, so find the width of colored paper strip. (accurate to 0. 1 cm) important process

Let the width of the color bar be x cm.

(x+ 18)(x+ 12)=( 18× 12)( 1+2/3)，

x？ +30x+2 16=360，

x？ +30x- 144=0，

x=(-b √b？ -4ac)/2a

≈- 15 19.2

≈4.2.

The width of the color bar is 4.2 cm.