Ask a math problem, eight in the math evaluation manual It is known that Y / x = 5 / 3 Find the value of Y / x + Y - Y / X - Y - x ^ 2 / y ^ 2 - x ^ 2

Ask a math problem, eight in the math evaluation manual It is known that Y / x = 5 / 3 Find the value of Y / x + Y - Y / X - Y - x ^ 2 / y ^ 2 - x ^ 2

y/x+y - y/x-y - x^2/y^2-x^2
=[Y(x-y)-y(x+y)+x^2]/(x+y)(x-y)
=x^2-2Y^2/x^2-y^2
∵y/x=5/3
∴y=5/3x
Original formula = [x ^ 2-2 * 25X ^ 2 / 9] / (x ^ 2-25 / 9x ^ 2) = 41 / 16

On the p23 page of the Handbook of the fifth grade evaluation of primary school mathematics
Among the four numbers of 2, 3, 4 and 7, there are () which can form true fraction by any two numbers, and the smallest true fraction is (); there are () which can form false fraction by any two numbers, and the largest false fraction is ()
The girl asked to answer in five minutes

Six, two out of seven, six, seven out of two

As shown in the figure, D is a point on the edge ab of △ ABC, DF intersects AC at point E, and AE = CE, FC ‖ ab

It is proved that: ∵ FC ‖ AB, ∵ DAC = ∵ ACF, ∵ ADF = ∵ DFC. Also ∵ AE = CE, ≌ ade ≌ CFE (AAS). ∵ de = EF. ∵ AE = CE, ∵ quadrilateral adcf is parallelogram. CD = AF

The determination of congruence of triangles in the first half of junior two
SSS (edge side) SAS (edge side) ASA (angle side) AAS (angle side) HL (bevel side, right angle side) need detailed explanation one by one (I don't understand any of them). What's the meaning of HL plus RT? And how to judge that it is edge, corner, edge and so on? How can you tell?

SSS in two triangles, three sides are equal, then the two triangles are congruent
SAS in two triangles, if both sides and their angles are equal, then the two triangles are congruent
ASA in two triangles, if the two corners and their edges are equal, then the two triangles are congruent
AAS in two triangles, two angles and one side are equal, then the two triangles are congruent
HL in two RT triangles (right triangles), if the hypotenuse and a right side are equal, then the two triangles are congruent
These are in the mathematics books of grade two. What's your junior year now? You can ask me if you don't understand

It is known that in △ ABC, CA = CB, ∠ C = 90 °, D is any point on AB, AE ⊥ CD, e for foot drop, BF ⊥ CD, f for foot drop. The proof is: EF = | ae-bf |

It is proved that: ∵ AE ⊥ CD, ∵ AEC = 90 °, ∵ ACE + ∠ CAE = 90 °, (the two acute angles of right triangle complement each other) ∵ ACE + ∠ BCF = 90 °, ∵ AE ⊥ CD, BF ⊥ CD, ∵ AEC = ∠ BFC = 90 ° in △ ace and △ CBF, ∵ AEC = ∠ BFC} C ∵

AB is parallel to CD, e is in AB, G is in CD, be = CG, connect BC, f is the midpoint of BC. It is proved that EFG is on a straight line
In the triangle ABC, the circumference of ABC is 15 and Bo is bisected

The first problem is that f is the midpoint of BC, so BF = cf. the congruence of two triangles can be proved by using the edges and corners. So f must also be the midpoint of eg, that is, EFG is on a straight line
It is suggested that the hypothetical method or the contrary method is more convenient
Because o is the heart, the distance from O to each edge is 2, that is, the radius of inscribed circle is 2
According to the formula r = (2 * s) / C
The solution is s = 15

As shown in the figure, it is known that be is equal to ABC, CE is equal to ACD, and be is given to E. verification: AE is equal to fac

Prove: as shown in the figure: the crossing points e are eg ⊥ BD, eh ⊥ Ba, EI ⊥ AC respectively, the vertical feet are g, h, I, ∵ be bisection ﹥ ABC, eg ⊥ BD, eh ⊥ Ba, ﹥ eh = eg. ∵ CE bisection ﹥ ACD, eg ⊥ BD, EI ⊥ AC, ﹥ EI = eg, ﹥ EI = eh (equivalent substitution), ﹥ AE bisection ﹥ fac (the point with equal distance to the two sides of the angle must be on the bisection line of the angle)

The condition that a quadrilateral is a diamond is ()
A) The diagonals are equal and equally divided
B) The diagonals are perpendicular and equal to each other
C) The diagonals divide equally
D) A set of diagonally equal and divided equally by a diagonal

The answer is that DA is a rectangle. It can be a rectangle or a square. But a rectangle is not a special rectangle. Only a square is a special diamond. B does not say that the diagonals are equally divided. Even a parallelogram is not a diamond. C is a parallelogram. D is a group of diagonals

Help me judge the following four sentences to see which are right and which are wrong
Better explain
1: A set of parallelograms whose opposite sides are parallel and whose opposite angles are equal are parallelograms ()
2: A quadrilateral whose adjacent sides are equal to each other is a diamond ()
3: A quadrilateral with four equal angles is a rectangle ()
4: A quadrilateral whose diagonals are perpendicular and equal to each other is a square ()

1: A group of parallelograms whose opposite sides are parallel and a group of diagonally equal are parallelograms (pairs). Because the opposite sides are parallel, the other groups of diagonally equal. 2: a quadrilateral whose adjacent sides are equal is a diamond (pair). If each adjacent side is equal, the four sides are all equal. 3: a quadrilateral whose four corners are equal is a rectangle (pair)

To judge right or wrong, write reasons
1. The two arcs opposite by equal central angles are equal
2. Divide the diameter of (I typed it in Pinyin) equally

1. X k may be the same arc
The diameter of the square is perpendicular to the square