2. The weather station of city a predicts that the center of typhoon is at point B, 300km east of city A. the typhoon moves 60 degrees north by West from point B at the speed of 10km per hour. The distance from the center of typhoon to 200km can be affected A city will be affected, through the calculation. A city will be affected for several hours Thank you very much Who has ever done the question that there are two people, a and B, each of whom goes twice, a buys 1000 kg each time, B buys 800 yuan each time, asking for the average of a and B, who is more affordable

2. The weather station of city a predicts that the center of typhoon is at point B, 300km east of city A. the typhoon moves 60 degrees north by West from point B at the speed of 10km per hour. The distance from the center of typhoon to 200km can be affected A city will be affected, through the calculation. A city will be affected for several hours Thank you very much Who has ever done the question that there are two people, a and B, each of whom goes twice, a buys 1000 kg each time, B buys 800 yuan each time, asking for the average of a and B, who is more affordable

Let's set point B to move along the line BC
If the angle ABC is equal to 30 ° according to the meaning of the title, then the place closest to a in the process of typhoon movement is the perpendicular foot D of the vertical section from a as BC, and from ab = 300 to ad = 150

Junior high school mathematics problem can't, ask which teacher to help solve
It's better to have a process
-4N + M = 2 m and N are reciprocal

-4n+m=2…… ①
And because m.n is negative reciprocal
So m = - 1 / N ②
Substitute (2) for (1)
－4n－1／n=2…… ③
③ The formula is multiplied by n
－4n²－1=2n

Swing is () rotation or translation phenomenon, slide is () rotation or translation phenomenon?

Swing is spinning
Slide is translation

Find the vector with the same angle of a = (7 / 2,1 / 2), B = (1 / 2,7 / 2) and the module length of 1

Let C = (m, n),
|c|=√（m^2+n^2)=1,
Let the angle between vectors a and C be θ
cosθ=a·c/(|a||c|=(7m/2+n/2)/[√（49/4+1/4）*1]=√2(7m/2+n/2)/5,
cosθ=b·c(/|b||c|)=(m/2+7n/2)/√[(1/4+49/4)*1]=√2(m/2+7n/2)/5,
√2(7m/2+n/2)/5=√2(m/2+7n/2)/5,
m=n,
m^2+n^2=1,
m=±√2/2,
n=±√2/2,
m. N should take the same sign
Then the vector C = (√ 2 / 2, √ 2 / 2), C = (- √ 2 / 2, - √ 2 / 2),

Known: as shown in the figure, ⊙ o, ab = AC, OD ⊥ AB in D, OE ⊥ AC in E

Connecting OA and extending BC to point F, ∵ o is the circumscribed circle of △ ABC, ∵ o is the outer center of △ ABC, ∵ AB = AC, ∵ AF is the vertical bisector of BC, ∵ BAF = ∠ CAF, ∵ OD ⊥ AB, OE ⊥ AC,