Solution: let this percentage be a.
200+200( 1+a)+200( 1+a)? = 1400
Let 1+a=t
t? +t-6=0
(t-2)(t+3)=0
T=2 or t=-3 (truncation)
So 1+a=2.
a= 1= 100%
14, with two numbers. Their sum is 13, and their product is -48. What are these two numbers?
Solution: Let one number be a and the other number be13-a.
a( 13-a)=-48
Answer? - 13a-48=0
(a- 16)(a+3)=0
A=-3 or a= 16
When a=-3, another number is 16.
When a= 16, another number is -3.
15. In order to expand the 1 swimming pool with a length of 200m and a width of 60m into a large water amusement park with a circumference of 600m, the length of the swimming pool is increased by xm. So when x =, the area of water swimming pool is 20000 square meters. If we can find the value of x? If you can't explain why.
Solution: after the length is increased, it is 100+x meters.
At this time, the width is (600/2- 100-x)=200-x meters.
( 100+x)(200-x)=20000
20000+200x- 100x-x? =20000
x? - 100x=0
x(x- 100)=0
X= 100 or x=0 (omitted)
The length is increased by 100m and the width is increased by 200- 100-60 = 40m.
16, Class 1, Grade 9, Group 2 At a party, each student presented a photo to the other students. This activity sent out 90 photos. How many students are there in this group?
Solution: There are X students.
Each student received x- 1 photo.
A * * * has x students.
Then the total number = number of students × number of photos received by each student.
The formula x(x- 1)=90.
x? -x-90=0
(x- 10)(x+9)=0
X= 10 or -9 (truncated)
So there are 10 students.
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