B ^ 2 + C ^ 2-B * C = a ^ 2 / C / b = 1 / 2 + root 3 in triangle ABC dial the wrong number B ^ 2 + C ^ 2-B * C = a ^ 2, C / b = 1 / 2 + root 3 in triangle ABC

B ^ 2 + C ^ 2-B * C = a ^ 2 / C / b = 1 / 2 + root 3 in triangle ABC dial the wrong number B ^ 2 + C ^ 2-B * C = a ^ 2, C / b = 1 / 2 + root 3 in triangle ABC

B ^ 2 + C ^ 2-bc = a ^ 2 from cosine theorem: B ^ 2 + C ^ 2-A ^ 2 = 2bccosa, so cosa = 1 / 2A = 60 degrees from sine theorem: C / b = sinc / SINB = 1 / 2 + √ 3sinc = SINB (1 / 2 + √ 3) sin (a + b) = SINB (1 / 2 + √ 3) sin (60 + b) = SINB (1 / 2 + √ 3) √ 3 / 2cosb + 1 / 2sinb = 1 / 2sinb + √ 3sinb √ 3 /

If cos (π / 4 + x) = 3 / 5,7 / 12 π

cos(π/4+x)=3/5
∴√2/2（cosx-sinx）=3/5
∴ cosx-sinx=0.6*√2
The square of both sides gives cosx ^ 2 + SiNx ^ 2-2sinxcosx = 18 / 25
∴sinxcosx=7/50>0
The same sign of SiNx and cosx, in one or three quadrants
And 7 / 12 π

1. Find the definition field of [SiNx (cosx)] under the function y = root
2. In known triangle ABC, Sina + cosa = 2 / 3, judge the shape of triangle ABC
3. If cosx + (cosx) square = 1, find the value of (SiNx) square + (SiNx) 6th power + SiNx) 8th power
4. Simplification: 1 + 3 (SiNx) square (secx) fourth power + (TaNx) sixth power
5. Calculation: sin15 degree + tan30 degree, cos15 degree (sum and difference formula of two angles)
The first is sin (COS), not SiNx * cosx

1. Is SiNx multiplied by cosx or sin (cosx)? 2, after the square of both sides of the equation: 1 + sin2a = 4 / 9sin2a = - 5 / 9180 ＜ 2A ＜ 36090 ＜ a ＜ 180, so it is an obtuse triangle. 3, from the known: (SiNx) ^ 2 = 1 - (cosx) ^ 2 = cosx (cosx) ^ 2 = 1-cosx (SiNx) square + (SiNx) 6th power + SiNx) 8 = co

Add all the 1000 natural numbers from 1 to 1000, and the sum is______ ．

According to the meaning of the title: in 1-999, each number of 1-9 appears 100 times in 100, 10, and one place, so in 1-999, the sum of all numbers is: (1 + 9) × 9 △ 2 × 100 × 3 = 13500; the sum of 1000 numbers is: 1 + 0 + 0 + 0 = 1; so the natural number 1 23 45 In 1000, the sum of all numbers is: 13500 + 1 = 13501

Find the sum of all the numbers of all the continuous natural numbers from 500 to 1000
Example: 521 = 5 + 2 + 1
It's better to write the formula

Thousand digit sum: 1
Sum of hundreds: (5 + 6 + 7 + 8 + 9) * 100 = 3500
Sum of ten digits: (1 + 2 + 3 +. + 9) * (500 / 10) = 2250
Sum of digits: (1 + 2 + 3 +. + 9) * (500 / 10) = 2250
Total number: 1 + 3500 + 2250 + 2250 = 8001

Mathematical Olympiad question: in the 1000 to 1999 natural numbers, how many thousands, hundreds, tens, exactly two of them are the same?

Among the natural numbers from 1000 to 1999, there are 1 * 9 * 8 * 7 = 504 kinds of thousand, hundred and ten digits, three kinds of single digits, nine kinds of same ones, 10001222, four kinds of single digits, one kind of same ones, 1111

How many digits are there among the 1000 natural numbers from 1 to 1000?
emergency

One single digit
Two digit 10 + 1 × 9 = 19, where 10 represents 1 of 10-19 tens and 1 × 9 represents 1 of 11-91 ones
Three digit 100 + 20 × 9 = 280, where 100 represents 1 of 100-199, 20 × 9 represents 10 of 100-999 and 1 of two digits
Four digits, because it's only 1000
So there are 1 + 19 + 280 + 1 = 301 ones

Put 40 grams of white sugar in 160 grams of white boiled water and turn it into sugar water. How much sugar accounts for

948940007,
40/(160+40)=1/5
Sugar accounts for 1 / 5 of sugar water

If you put 5 grams of sugar into 60 grams of water, how many parts of sugar is equal to one thirteenth

5/5+60=1/13

Put 11 grams of white sugar into 100 grams of water. What's the percentage of sugar in water?

Put 11 grams of white sugar into 100 grams of water. Sugar is 11 / 100 of water, and sugar accounts for 11 / 111 of water