As shown in the figure, the right angle vertices of a pair of triangular plates are overlapped and placed on the desktop. If ∠ AOD = 150 °, then ∠ BOC=______ °．

As shown in the figure, the right angle vertices of a pair of triangular plates are overlapped and placed on the desktop. If ∠ AOD = 150 °, then ∠ BOC=______ °．

∫∠ AOB = ∠ cod = 90 °, and ∠ AOD = 150 °∠ BOC = ∠ AOB + ∠ cod - ∠ AOD = 90 ° + 90 ° - 150 ° = 30 °. So the answer is: 30

As shown in Fig. 1 and 2, two right angle vertices o of two identical triangular plates are overlapped and placed as shown in Fig. 1 and 2. (1) if ∠ BOC = 60 ° as shown in Fig. 1, guess the degree of ∠ AOD; (2) if ∠ BOC = 70 ° as shown in Fig. 2, guess the degree of ∠ AOD; (3) guess the relationship between ∠ AOD and ∠ BOC, and write the reasons

(1) The results show that ∫ AOB = 90 °, BOC = 60 °, AOC = ∫ AOB - BOC = 90 ° - 60 ° = 30 °. And ∫ cod = 90 °, AOD = ∫ AOC + cod = 30 ° + 90 ° = 120 ° (2) ∫ AOB + cod + BOC + AOD = 360 °, AOB = 90 °, COD = 90 °, BOC = 70 ° and ∫ Ao

Use 5 1, 5 2, 5 3, 5 4, 5 5, 5 6, 5 7, 5 8, 5 9 column formulas to calculate 100, for example 111-11 = 100
You can use any operation, including addition, subtraction, multiplication, division, square, bracket, root, log, factorial, etc
The meaning of the title is to use 5 same numbers to list 9 formulas, so that these 9 formulas are equal to 100, for example
111-11 = 100, only the number 1 can appear in the formula, and for example, (2 * 2 * 2 + 2) ^ 2 = 100

5 * 5 * 4 * (power of other numbers of 1)

What does (- 39 / 8) - (- 11 / 2) + (- 17 / 4) - (- 25 / 8) equal

Original formula = - 39 / 8 + 44 / 8-34 / 8 + 25 / 8
=-4/8
=-1/2

（-39/8）-（-11/2）+（-17/4）-（+25/8）=

(- 39 / 8) - (- 11 / 2) + (- 17 / 4) - (- 25 / 8) = - 39 / 8 + 11 / 2-17 / 4-25 / 8 = - 64 / 8 + 5 / 4 = - 8 + 2-3 / 4 = - 6 and 3 / 4

How to read the formula (25 + 17) * 8
Can you read it like this? Will reading 25 + 17 + 8 increase children's learning difficulty?

The sum of 25 and 17 times 8

Look at the rules of these groups of numbers: (1) 6, (2) 9, (3) 13 (4) 18. What's their leading formula

a1=6 a2=9 a3=13 a4=18
a2-a1=3
a3-a2=4
…… a（n）-a（n-1） =n+1
The difference is 3.45, which is equal
a（n）-a（n-1） =n+1
Add it all up
an-a1=3+4+5+…… n+1
an=6+（n+4）（n-1）/2
=N square / 2 + 3N / 2 + 4

How to do 1 + 2 + 3 + 4 +. + 36 + 37 + 38 + 39 + 40

Write = (1 + 40) * 40 / 2 = 820 with the summation formula of arithmetic sequence

How to calculate (40 + 38 + 36 +... + 4 + 2) - (39 + 37 + 35 +... + 3 + 1)

(40+38+36+...+4+2)-(39+37+35+...+3+1)
=40+38+36+...+4+2 - 39-37-35-...-3-1
=40-39+38-37+36-35+…… +4-3+2-1
=1+1+1+…… +1+1
It's 20 ones in all
=20

In a subtraction formula, the sum of the subtracted, the subtracted and the difference is 168. The ratio of the difference and the subtraction is 3:4. What are the differences and the subtractions?

Because: subtraction + difference = subtracted, so: subtracted + subtraction + difference = subtracted + subtracted = 168, subtracted = 168 △ 2 = 84
That is to say, the sum of subtraction and difference is 84. Then we know that the ratio of difference and subtraction is 3:4, and we just distribute 84 in proportion. 84 ÷ (3 + 4) gets a share, and then we multiply 3 and 4 to get the difference and subtraction respectively