Italian scientists in the 17th century______ On the basis of experiments, it is concluded by reasoning that if the surface of an object moving on a horizontal plane____ The object is resisted____ The speed of the object will remain the same and it will move forever 2. The two objects a and B are stacked on a smooth horizontal plane. If the wood block a is pulled horizontally with a tensile force of 10N, and the wood block a and B remain stationary, the object a will be damaged___ N. Direction___ The friction of B is affected___ N. Direction___ The friction between the two parts is very strong 3. A force is 5N and a force is 15N. The resultant force of these two forces cannot be () A.5N B.10N C.15N D.20N

Italian scientists in the 17th century______ On the basis of experiments, it is concluded by reasoning that if the surface of an object moving on a horizontal plane____ The object is resisted____ The speed of the object will remain the same and it will move forever 2. The two objects a and B are stacked on a smooth horizontal plane. If the wood block a is pulled horizontally with a tensile force of 10N, and the wood block a and B remain stationary, the object a will be damaged___ N. Direction___ The friction of B is affected___ N. Direction___ The friction between the two parts is very strong 3. A force is 5N and a force is 15N. The resultant force of these two forces cannot be () A.5N B.10N C.15N D.20N

Italian scientists in the 17th century_ Galileo_____ On the basis of experiments, it is concluded by reasoning that if the surface of an object moving on a horizontal plane_ Absolutely smooth___ The object is resisted_ Zero___ The speed of the object will remain the same and it will move forever
3. A force is 5N and a force is 15N. The resultant force of these two forces cannot be (a)
A.5N B.10N C.15N D.20N

A passenger travelling by train honked his horn for the first time when the train was some distance in front of a tunnel entrance. Three seconds later, he heard the echo. At this time, the train honked its horn for the second time. This time, only two seconds later, he heard the echo. He tried to find the distance from the tunnel entrance and the speed of the train when the train honked its horn for the first time

The distance is s
Then: 2s-3v = 340 * 3
2（S-3V）-2V=340*2
The solution is s = 408M
V=68m/s

In the cuboid abcd-a1b1c1d1, ab = 3, ad = 4, Aa1 = 5, then the angle between the straight line AC1 and the plane ABCD is 0______ ．

Connect AC, then ∠ c1ac is the angle between straight line AC1 and plane ABCD ∵ AB = 3, ad = 4, ∵ AC = 5, ∵ Aa1 = 5, ∵ c1ac = 45 degrees, so the answer is: 45 degrees

Given a 2 - 3A + 1 = 0, find the value of a 2a4 + 1

Then a + 1A = 3a2a4 + 1 = 1A2 + 1A2 = 1 (a + 1a) 2 − 2 = 17. A: the value of a2a4 + 1 is 17

Given the points a (1,1), B (2,2) and P on the straight line y = 12x, find the coordinates of point P when | PA | 2 + | Pb | 2 gets the minimum value

Let P (2t, t), then | PA | 2 + | Pb | 2 = (2t-1) 2 + (t-1) 2 + (2t-2) 2 + (T-2) 2 = 10t2-18t + 10. When t = 910, the minimum value of | PA | 2 + | Pb | 2 is obtained. When p (95910) | PA | 2 + | Pb | 2 has the minimum value, the coordinate of P point is (95910)

1 + 0.45/0.9-7 / 8 (simple calculation) calculation process
It's 1 + 0.45 △ 0.9-7 / 8

1+0.45/0.9-7/8
=1+1/2-7/8
=12/8-7/8
=5/8
If you don't understand this question, you can ask,

If the generatrix of a cone is 5 cm long and the diameter of its bottom is 6 cm, the surface area of the cone is 0______ Cm 2 (π is reserved for the results)

Surface area of cone = π × 32 + π × 3 × 5 = 24 π cm2

There are eight numbers, 59, 23, 0.5113252447, and 0.5.1 are six of them. If the fifth number is 0.5.1 in descending order, then the third number is 0.5.1 in descending order___ ．

① 59 = 0. · 5, ② 23 = 0. · 6, ③ 0.51, ④ 1 325 = 0.52, ⑤ 2 447 ≈ 0.5106, 6 6 0.5 ·· 1, if the fifth number is 0.5 ·· 1, the fourth number is 0.5 ·· 1 in the order of big to small: 0. · 6 ＞ 0. · 5 ＞ 0.52 ＞ 0.5 ·· 1 ＞ 0.5106 ＞ 0.51, that is, 23 ＞ 59 ＞ 1 325 ＞ 0.5 ·· 1 ＞ 2 447 ＞ 0.51, the third number is: 1 325

The tangent equation from point P (1, - 2) to circle x2 + y2-6x-2y + 6 = 0 is______ ．

Circle x2 + y2-6x-2y + 6 = 0 is transformed into the standard equation, and (x-3) 2 + (Y-1) 2 = 4. The center of the circle is C (3,1), and the radius is r = 2. When the line passing through point P (1, - 2) is perpendicular to the X axis, the equation is x = 1, and the distance from the center of the circle to the line is equal to the radius. At this time, the line is tangent to the circle, which is in line with the meaning. When the line passing through point P (1, - 2) is not perpendicular to the X axis, let the equation be y + 2 = K (x-1) ）That is, kx-y-k-2 = 0, the distance from circle C to the straight line d = R, we get | 3K − 1 − K − 2 | 1 + K2 = 2, the solution is k = 512, the equation of the straight line is y + 2 = 512 (x-1), and the simplification is 5x-12y-29 = 0

Given two points P (0,1) and Q (1,0), if the image of quadratic function y = x ^ 2 + ax + 3 intersects with line segment PQ, the value range of real number a is obtained

First of all, the equation of line PQ is required, and its slope is calculated. From the slope formula, we can know that: k = (0 - 1) / (1 - 0) = - 1, so from the point oblique formula, we can get the linear equation as: y = - (X - 1) = - x + 1 (1) Because it is to find the point of intersection, we connect (1) with the image of quadratic function y = - x +