(1) Can the duck farm area reach 150250 square meters? Can it reach 200 square meters?
(2) Can it reach 250 square meters?
Analysis:
In this problem, one side of a chicken farm can be set, and then the area of the chicken farm can be represented by an unknown number according to the area of a rectangle = length × width. If the area of chicken farm is required to reach 150 square meters, the area of chicken farm should be made equal to 150 square meters first, and then the equation should be solved. If so, it is proved that it can reach 150 square meters. If the equation is not understood, it means that it cannot reach 65,440 square meters.
Solution: (1) Let the side parallel to the wall be x meters and the side perpendicular to the wall be 1/2(40-x) meters, according to the meaning of the question.
①
1/2x×(40-x)= 150
x？ -40x+300=0，
a= 1，b=-40，c=300
∵b？ ; -4ac = 1600- 1200 = 400 > 0，
It can reach 150 square meters.
x？ -40x+300=0，
(x- 10)×(x-30)=0
∴x= 10 or x=30
1? /2 (40-x) = 15m or 1? /2 (40-x) = 5m
② If
1/2x×(40-x)=200，
x？ -40x+400=0，
That is, (x-20)2=0,
The solution is x 1=x2=20,
∴
1/2(40-x)= 10，
It can reach 200 square meters.
(2) If you let
1/2x×(40-x)=250，
And then x? -40x+500=0，
∵b？ -4ac