Math problems need a detailed process Thank you for the rush 10

28、d29、b

30、b31、c

32、d33、c

34、c35、c

36、a37、d

38, B I'm sorry, I'm going to sleep, it's too late for the detailed process.

28. b The first try should be 3 times, and the last one should be opened.

The second attempt was made 2 times and finally opened.

The third time try 1 time, the last one is opened, and the last one is not tried.

3 + 2 + 1 = 6.

29. The working efficiency of B A is 1 2, and B is 1 4

A completes 1 2 in one day, and the remaining 1 2 divided by B's 1 4 = 2 takes two days.

30. 10 catties of B fish can be exchanged for 21 catties of beans, indicating that 1 catty of fish needs 27 catties of beans.

12 catties of fish can be exchanged for 7 catties of meat, which means that one catty of meat costs 12 7 catties of fish 90 7 12 7 = catties of meat.

2 catties of oil for 5 catties of meat Explain that 1 catty of oil should be catties of meat and catties of oil.

31. C to try, take the smallest, this question is time 8 * 60 * 4 10 = 192

32, 10 (2 5-1 3) = 10 (1 15) = 150.

33. C 150 10=15km indicates that the speed sum is 15km

15 (1+2 3)=9 B's velocity.

34, c 5 * 100 2 = 250 grams 1000 (100 * 5) = 2 12 2 (is two grapefruit according to the price of apples but twice as expensive is 2 times, so *2) * 2 = (two grapefruits) 2 = 6 (one grapefruit) 18 6 = 3

35. c The balance is tilted in the direction of the heavy so we can know.

a+b=c+d a+d>b+c b>a+c (excluding a).

Add the above two to get a+a+b+d>c+c+b+d according to the same magnitude of the same subtraction, the direction remains the same to get a+a>c+c and thus get a>c exclusion d

Look at the first a+b=c+d a>c b>c so d max choose c

36. To be exact, you can't do these four, it should be 45.

37. D Day 1 Day 2 2 Day 1 2 Day 3 1 2*2 3=1 3 Day 4 1 3*3 4=1 4 So the first day is a fraction.

One in 30 (1 30) is 30 days.

38, b 12 (120+30=150.

I would venture to ask, isn't this formula equal to 767 in the end, and if not, I can't figure it out.

Let me talk about the idea, the curly braces should be added after the multiplication sign, the small brackets should be added to whom, start with the large number at the end, start with the small brackets, such as the last 6 * 7 + 8 * 9, if you add brackets, it is 6 * (7 + 8) * 9 The result is directly greater than 777, so this possibility is excluded, it is through the method of trying this way to finally get the answer, there is a singular number of 777, it is very likely that 1 is a single number, first subtract 1 to try, 2 is very likely to multiply the entire latter formula by 2, So ignore 2 for now, look at the formula that follows, and finally 1+2*{(3+4*(5+6)*7+8*9} 767

Maybe it's not right, you try this idea, sorry I can only help you here.

Solution: Let the coordinates of the m point be (x,y) and o be the coordinate origin.

then, om = under the root sign (x squared plus y squared).

And because y=-1 x

So y square = 1 x squared.

So om = under the root number (x square plus 1 x squared) bridge brigade.

Again, the minimum value of x square plus 1 x square is 2, so om = 2 under the root number

From the symmetry, we can get mn=2 times to cancel this root number under 2

The image doesn't seem right. The inverse proportional function y=1 x can only pass 2 4 quadrants??? That is, over the origin?

Solution: The straight line l passes through the origin, so we can assume that its representation equation is: y=kx, and the straight line intersects with the image of the inverse proportional function y=-1 x at the two points m,n, then.

kx==-1/x

The above equation has x 2=-1 k;

To be satisfied, there is a solution such as, so k<0;

So, x1=(-1 k) (1 2),x2=-(1 k) (1 2), 1).

Let m(x1,y1),n(x2,y2).

So, mn 2=(y1-y2) 2+(x1-x2) 2

y1^2+y2^2-2y1y2+x1^2+x2^2-2x1x2

kx1)^2+(kx2)^2-2kx1kx2+x1^2+x2^2-2x1x2

k^2+1)x1^2+(k^2+1)x2^2-2(k^2+1)x1x2

4(1+k^2)/k

4(1/k+k)

So when mn is the smallest, k=-1

At this point, mn=8 (1 2).

Oh,That's probably the process of the solution.,Because the formula here is not good to represent the clever head.,It looks more complicated and filial piety.,If you don't understand, you can ask me directly.。。。

1. Easy to know abc=180-(90-30)-30=90cos abc=cos( 2)=0

again ab = 10 km

bc=19 km

Cosine theorem: ac = ab + bc -0

ac= km

2、tan∠cab=bc/ab

cab=c is east-northerly of a.

Let the slope of the line be k, then the equation is y=k(x-1), i.e., kx-y-k=0 tangent, then the distance from the center of the circle (0,0) to the straight line d=|0-0-k|Root number (k +1) = 1

k|= The root number (k +1) is squared on both sides.

k = k +1, k does not exist.

The slope does not exist, i.e. the equation for the straight line l is x=1

Such as the envy of the limbs, the withered Tu Lina shoot.

<> please congratulate the annihilation of the limbs and change the number of the number of Zen worlds.