As shown in the figure, the area of parallelogram is 20 square centimeters, and the area ratio of triangle a, B and C in the figure is______ The area of the shadow is______ Square centimeter

As shown in the figure, the area of parallelogram is 20 square centimeters, and the area ratio of triangle a, B and C in the figure is______ The area of the shadow is______ Square centimeter

According to & nbsp; the area of parallelogram = bottom × height & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; height = the area of parallelogram △ bottom = 20 ÷ (2 + 3) = 20 ÷ 5 = 4 (CM) & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; according to & nbsp; the area of triangle = bottom × height △ 2 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; The area of triangle a = (2 + 3) × 4 / 2 = 20 / 2 = 10 (cm2) & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; the area of triangle B = 2 × 4 / 2 = 8 / 2 = 4 (cm2) & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; the area of triangle C = 3 × 4 / 2 = 12 / 2 = 6 (cm2), then a: B: C = 10:4:6 = (10 / 2): (4 / 2): (6 / 2) = 5:2:3, so fill in 5:2:3, 4

As shown in the figure, there are two kinds of______ The number of triangles______ A parallelogram______ It's a trapezoid

① There are 9 small triangles and 3 triangles composed of 4 triangles in the figure, so there are 9 + 3 + 1 = 13 triangles in total; ② there are 2 parallelograms in the second layer, 6 parallelograms in the third layer, 4 parallelograms in the combination of the second and third layers, 1 parallelograms in the combination of the first and second layers, 2 parallelograms in the combination of the first and second and third layers, so there are 2 + 6 + 4 + 1 + 2 = 15 parallelograms in total There are 1 + 4 + 7 + 2 + 4 = 18 trapezoids in the second layer, 4 trapezoids in the third layer, 7 trapezoids in the second and third layer, 2 trapezoids in the first and second layer, and 4 trapezoids in the first and second and third layer

How many triangles, parallelograms and trapezoids are there in the figure below?

How many triangles, parallelograms and trapezoids are there in the figure below

The proof of right triangle in Junior Three
Let the two right sides of a right triangle be a and B respectively, and the hypotenuse be c. let a, B and C be natural numbers and a be prime numbers. It is proved that 2 (a + B + 1) must be a complete square number

The three sides of the triangle are a.b.c
And a & sup2; - BC = a (B-C), then what kind of triangle is this triangle classified by edge?

Let a ^ 2-bc = AB AC a ^ 2-AB = - AC + BC a (a-b) = - C (a-b) a (a-b) + C (a-b) = 0 (a-b) (a + C) = 0, so a = B or a = - C (rounding off) because a = b, so the triangle is isosceles triangle

According to the proposition "the bisectors of adjacent complementary angles are perpendicular to each other", draw a figure, write the known, verify and complete the proof

 
As shown in the figure above, ∠ 1 + 2 + 3 + 4 = 180 degree
AB and BC are bisectors of (∠ 1 + 2) and (∠ 3 + 4) respectively
Therefore, 1 = 2; 3 = 4
The adjacent complementary angles are ∠ 2 and ∠ 3
∠2+∠3=（∠1+∠2+∠3+∠4）/2=90°
So ab ⊥ BC
The conclusion that the bisectors of adjacent complementary angles are perpendicular to each other is true

Place two right angle triangular plates with 30 ° angle as shown in the figure, point D on BC, connect be, ad, and the extension line of ad intersects be at point F. ask if AF and be are vertical? And explain the reason

It is proved that AF ⊥ be. ∵ ∠ ABC = ∠ Dec = 30 °, ∠ ACB = ∠ DCE = 90 °, ∵ △ ABC ∽ Dec ∩ BCEC = ACDC, ∵ △ BCAC = ECDC. ∵ △ DCA ∽ ECB. ∵ DAC = ∠ EBC. ∵ ADC = ∠ BDF, ∵ EBC + ∠ BDF = ∠ DAC + ∠ ADC = 90 °. ∵ BFD = 90 ≁ AF ⊥ be

Primary school two circles, two painted circles, two triangles, a star, a heart-shaped horizontal line, two vertical lines, two rectangles

1. A body
The two circles are wheels, the triangle is parallel, and the line is up and down
2. Two electric lights,
3. A tree, with a round moon in the sky, can be a shadow on the ground
4. Chemical flasks
5. Teapot

What can two circles, two triangles and two parallel lines form
Design a meaningful graphic with commentary

Face
Two eyes, two eyebrows, one nose

One triangle is composed of three circles, two triangles are composed of six circles, and three triangles are composed of ten circles,
How many circles does the tenth triangle consist of? How many circles does n triangle consist of?

a1=3,a2=a1+3,a3=a2+4,…… , an = a (n-1) + (n + 1)
By adding the above formulas, we can get the conclusion
an=3+[3+4+… +（n+1）]
That is, an = 3 + (n-1) (n + 4) / 2
So A13 = 3 + (13-1) * (13 + 4) / 2 = 105