The equation S=(v+3)* 10 can be obtained.
It takes less than 12 hours to return from b to a at a constant speed.
The equation s < (v-3) * 12 can be obtained.
At the same time know v < 3 or v > 33.
2. solution: let the original length of the spring be x and the forward coefficient be k.
Then k( 16.4-x)=2kg.
K( 17.9-x)= 5 kg
Get k = 2000n/m.
X =15.4cm.
3. Solution:
Let x, y, z, y and z represent 1 angle, 5 angle and 1 yuan respectively.
There are:
x+5y+ 10z=70( 1)
x+y+z= 15 (2)
X, y, z Y, z are all integers, which do not exceed the total 7 yuan.
( 1)-(2) De: 4y+9z=55
Because y z is a positive integer, let x = 0x = 1x = 2x = 3. ...
x= 10
X=5 y=7 z=3 can be found.
4. Solution:
Suppose I bought x rabbits a year ago.
x+2 & lt； =2/3(2x- 1)
x+2 & lt； = 4/3-2/3
1/3x >=8/3
X & gt=8
That is to say, I bought at least eight.