8. The bottom of a triangle board is 26 decimeters, 14 decimeters less than the height. What is the area of this triangle board

S=26*(26+14)/2=520dm².

Prime numbers within 20 are (), where () is even

Prime numbers within 20 are (2, 3, 5, 7, 11, 13, 17, 19), where (2) is even
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The top of trapezoid is 8 cm, the bottom is 15 cm, and the height is 10 cm. The largest triangle is cut inside. The area of triangle is () square cm

If the triangle is required to have the largest area, the bottom should be the longest and the height should be the highest. Therefore, the maximum area of the triangle is the length of the bottom of the trapezoid and the maximum height is the height of the trapezoid
1 / 2 * 15 * 10 = 75 square centimeter

As shown in the figure, point a is a point on the circle O with the diameter of line segment BC, ad ⊥ BC is at point D, crossing point B as the tangent line of circle O, intersecting with the extension line of Ca at point E, point G is the midpoint of AD, connecting CG and extending to be, intersecting at point F, extending AF and the extension line of CB intersecting at point P. (1) verification: BF = EF; (2) verification: PA is the tangent line of circle o

It is proved that: (1) BC is the diameter of the circle O, be is the tangent of the circle O, EB ⊥ BC, ad ⊥ BC, ad ∥ be. We can get △ BFC ∽ DGC, △ FEC ∽ GAC. Bfdg = cfcg, EFAG = cfcg, bfdg = EFAG

If ∠ AOB is known, passing point O is used as ray OC, and OM bisects ∠ AOB (1) when OC is inside ∠ AOB, as shown in the figure, verify ∠ mon = 1 / 2 ∠ AOC (2) when OC is below OA, guess
Think about the quantitative relationship between ∠ mon and ∠ AOC, draw an image and explain it

In other words, if you do two rays through point O, it's not equal. It should be equal. According to the conditions you give me, I really can't draw a suitable graph. Can you provide the graph related to the topic first? No, in addition, where's point n

As shown in the figure, the diameter of ⊙ o is CD = 5cm, AB is the chord of ⊙ o, ab ⊥ CD, the perpendicular foot is m, OM: od = 3:5______ ．

The diameter of ∵ o is CD = 5cm, ∵ od = OC = 12CD = 12 × 5 = 52 (CM), ∵ om: od = 3:5, ∵ om = 35 × 52 = 32 (CM), connecting OA, ∵ ab ⊥ CD, ∵ AB = 2am. In RT △ OAM, oa2 = om2 + AM2, that is, (52) 2 = (32) 2 + AM2, the solution is am = 2 (CM). ∵ AB = 2am = 2 × 2 = 4 (CM)

Why can the solution of equation x ^ 2 + 2x + 1 = 0 form a set

Set is artificially defined, and inequality has set type, such as inequality X & # 178; - 2x-3

A point Q on the curve X ^ 2-y ^ 2 = 1 leads to the vertical line of the straight line L: x + y = 2, and the vertical foot is n?
Do you want to remove the points (5 / 4,3 / 4)

Let Q (x1, Y1), P (x, y), ∵ QN ⊥ L: y = - x + 2 ① The equation of line QN: y = x-x1 + Y1 ② The coordinates of point n are xn = (x1-y1 + 2) / 2, yn = (2-x1 + Y1) / 2, x = (x1 + xn) / 2 = (3x1-y1 + 2) / 4, y = (Y1 + yn) / 2 = (3y1-x1 + 2) / 4, that is, X1 = (3x + Y-2) / 2

How to transform a quadratic equation of two variables into an algebraic expression of one unknown to express another unknown?
Given the equation 2x-3y = 9, please deform the equation according to the following requirements:
1. Express y with algebraic expression containing x
2. Express x with algebraic expression containing y
Thinking: what is the essence of equation deformation?

1、Y=（2x-9）/3
2、X=（3y+9）/2

As shown in the figure, in ▱ ABCD, the diagonal AC = 21cm, be ⊥ AC, the perpendicular foot is e, and be = 5cm, ad = 7cm, then the distance between AD and BC is______ cm．

Let the distance between AD and BC be xcm, ∵ be ⊥ AC, ∵ s △ ABC = 12 · AC · be = 12 × 21 × 5 = 1052cm2, ∵ s ▱ ABCD = 2S △ ABC = 105, ∵ ad · x = 105, ∵ x = 15, that is, the distance between AD and BC is 15cm

8. The bottom of a triangle board is 26 decimeters, 14 decimeters less than the height. What is the area of this triangle board