One train is from Nanjing to Wuxi. The known distance is 200 km. Train a starts at 4 p.m. and runs at 45 km / h. the other starts at 3 p.m. and runs from Wuxi to Nanjing at 60 km / h. ask when the two trains will meet (round to the nearest minute)!

The other train set off for an hour first. In this hour, the other train went 60 kilometers by itself, and then the two trains set off. That is to say, starting from four o'clock, the two trains set off at the same time and met 80 minutes later
200-60 * (4-3) / (45 + 60) = 4 / 3 hours = 80 minutes
The time between them is 5:20

Proof: two of the quadratic equation (x-m) (x-m-n) = 1 are greater than m and less than m respectively

(x-m)(x-m-n)=1
(x-m)(x-m-n)-1=0
(x-m)^2-n*(x-m)-1=0
Let y = x-m, using the Veda theorem, we get that the multiplication of two roots of Y is equal to - 1, that is to say, one is greater than 0 and the other is less than 0
Then the two parts of the original equation are equal to m + y, that is, greater than m and less than m respectively

Given that the straight line L: x + my + 4 = 0, the circle C: x ^ 2 + y ^ 2 + 2x-6y + 1 = 0 has P and Q points symmetric with respect to L, and satisfies OP vector · OQ vector = 1, the equation for finding the straight line L (o is the origin)

On the circle C: x ^ 2 + y ^ 2 + 2x-6y + 1 = 0, P and Q are symmetric with respect to L
So the line L: x + my + 4 = 0 passes through the center of the circle (- 1,3),
So - 1 + 3M + 4 = 0,
The solution is: M = - 1
So the equation of line L is: X-Y + 4 = 0

One train is from Nanjing to Wuxi. The known distance is 200 km. Train a starts at 4 p.m. and runs at 45 km / h. the other starts at 3 p.m. and runs from Wuxi to Nanjing at 60 km / h. ask when the two trains will meet (round to the nearest minute)!