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is the end point of the faint line, description:o Point is on the equator.

o 18 o'clock at the point and 18 at all points on the L meridian.

80°E divides the two dates, and it is not a 180° meridian, so it is a natural date line, and the local time is 0.

Knowing the time difference between the two meridians, we can calculate that the time difference is 80° east longitude to 90° west, that is, 10° west longitude

If you are on the dusk line with O, you must be on the morning line, and when you are at sunrise at the sunrise at the place of O, you will also be on the sunrise at the time of the sunrise, and at 6 o'clock on the place of O, it will be 6 o'clock on the point of m, and it will be 6 o'clock on the place of M (the difference between the two places is 12°, and one degree is 4 minutes).

14.The polar day appears in place A, so the latitude range of place A is (66 ° 34, 90 °), the noon sun altitude angle is 40 °, the noon sun altitude angle = 90 ° - latitude difference, latitude difference = 50 °, A is at the northernmost end of the morning and dusk line, now assume that A is always the northernmost point of the morning and dusk line, then when the latitude difference between A and the direct sun point is the largest, it is at the direct equator of the sun, and A is at the North Pole, whenever the direct sun point moves one degree to the north, the latitude of A moves one degree to the south, and now the latitude difference between the two places is 50 degrees, which can be launchedWhen the direct point of the sun is 20° to the north and the first place moves 20° to the south, the latitude difference between the two places is 50°, which is the situation in the title, so the latitude of the first place is 70° north latitude.

In the diagram of the polar day in the northern hemisphere, the meridian where the northernmost point under the morning and dusk is located bisects the night hemisphere, that is, 120°E, then the 60°W opposite it bisects the day hemisphere, so the direct point of the sun is 60°W, and the direct point of the sun is 70°N, so the coordinates of the direct point of the sun (60°W, 20°N).

15.The direct sunlight is 20°N, the altitude angle of the second sun is 10°, the latitude of B is 80°N, and the altitude angle of the sun at noon is 30 degrees.

It is the midpoint of the dusk line, so it is a point on the equator. 80°E on the east side of the 9th, west side of the 8th, that is, 80°E is 0, its east side of 90° is the intersection of the dusk line and the equator (point O), so 80°E + 90° = 170°E

12. CMN is the dusk line, and the O point is on the equator, which is 18 o'clock at this time. From the O to the east, after 90° longitude (time difference of 6 hours) to 80°E, the longitude of the O place is 10°W.

13、d；o point is located on the equator, sunrise at 6 o'clock and sunset at 6 o'clock. Based on the longitude difference, the sunset at m o'clock 6:48 is calculated. The sunset time of M is 48 minutes later than that of O, and the sunrise time is 48 minutes earlier than that of O, which is 5:12 sunrise of M place.

14、a；The altitude of the Sun at noon, the lowest latitude for the occurrence of the polar day, is 40°, and according to the formula, the direct point of the Sun on that day is calculated to be 20°N.

15、d；The direct point of the sun is located at 20°n, and the midnight solar altitude is 10°, and the midnight solar altitude = local latitude - the lowest latitude at which the polar day occurs. It is calculated that the height of the sun at noon is 80°, and according to the formula, the altitude of the sun is 30°

14 questions x = 3, y = 2, the number of generations is over.

The conventional solution to this problem is to let the slope of ab be k, then the slope of ac is -k, because the coordinates of point a can be found, so you can calculate the straight line equation of ab, ac, the simultaneous elliptic equation uses the relationship between the two coordinates to calculate the coordinates of another intersection point in the slope, I have calculated, the calculation process is too complicated, it is easy to make mistakes, because it is a fill-in-the-blank problem, you can easily calculate it, the observed two straight line equations, from the analysis of the problem, the slope found has nothing to do with the value of k, so it can be assumed that k = 2, then yab = 2x, yac = - 2x+8 2 3, so that the coordinates of b and c are much easier to find, and the result of my calculation is b (-4 3, -4 2 3), c (92 27, -20 2 27) slope is 7 2 16

Hello, you have asked too many questions for the top students to answer for you. Don't forget to ask one question at a time!

Because the opening is upward, as long as f(1)<0 and f(2)<0 are satisfied.

Integrity first, pick first, I'll send it to you as soon as I'm done.

The problems are simple solutions to the system of equations, you can use the substitution method and the elimination method, the elimination method is relatively simple, but if you don't know how to bring it directly, just like the first question of 13 questions, the first y = what, bring in the second x + 2y = 8 in the y, you will get the unary equation about x, you will definitely do it, the rest are the same, transform an equation into x = what or y = what, substitute the second equation, become a unary equation, As for the 15th problem, I first treat a as a constant, and then use the method I said before to solve x,y, because x,y is positive, so x,y is greater than zero, and two inequalities are obtained, and the range of a is obtained by solving the inequality.

2mn-3m+6-2n, it can be solved in one step directly, without steps.