It is known that a, B and C are the three sides of triangle ABC and satisfy a ^ 2 + B ^ 2 + C ^ 2-ab-bc-ac = 0. Try to judge the shape of △ ABC

It is known that a, B and C are the three sides of triangle ABC and satisfy a ^ 2 + B ^ 2 + C ^ 2-ab-bc-ac = 0. Try to judge the shape of △ ABC

a^2+b^2+c^2-ab-bc-ac
=1/2[(a-b)^2+(b-c)^2+(c-a)^2]=0
(a-b)^2+(b-c)^2+(c-a)^2=0
a-b=0
b-c=0
c-a=0
a=b=c
ABC is an equilateral triangle

A word that starts with a K for a number
1000000 starts with m and how much with k

One million is one million
1000 is sometimes referred to as 1K
K is the abbreviation of kilo, 1kg = 1000g = 1kilo gram, that's how it comes

In the triangle ABC, the opposite sides of angle ABC are A.B.C, and AC = the square of a + the square of C-The square of B
（1） Finding the size of angle B
（2） If ‖ Ba vector BC vector ‖ = 2, find the maximum area of triangle
Answer questions seriously, I'll go back at noon to give you bonus points

1. According to the cosine theorem, CoSb = (a ^ 2 + C ^ 2-B ^ 2) / 2Ac = 1 / 2
Therefore, B = 60 degree
2. According to the parallelogram rule: ∣ Ba vector BC vector ∣ = ∣ CA vector ∣ = 2
That is: B = 2
Substituting into the known equation: AC = a ^ 2 + C ^ 2-4
Because a ^ 2 + C ^ 2 ≥ 2Ac, AC = a ^ 2 + C ^ 2-4 ≥ 2ac-4
That is: AC ≤ 4
SINB = (√ 3) / 2
So s (△ ABC) = (1 / 2) AC &; SINB ≤ (1 / 2) × 4 × (√ 3) / 2 = √ 3
In this case, a = b = C = 2

Choose a phrase that has the same or similar meaning as the underlined part of the sentence
——Will you please reply to the letter as soon as possible?
——No problem.
A.write to B.answer C.hear from D.recieve
The line drawing part is reply, not reply to

Choose B
Reply = answer = answer

From the five natural numbers of 3, 13, 17, 29 and 31, take two numbers at a time as the numerator and denominator of a fraction respectively, and they can be formed______ A minimalist score

The number of the simplest fractions: 5 × (5-1) = 20

The + (?) denotes the same kind of person or thing. Is it singular or plural
Private cars are very popular
the private car(s) is(are) very popular！
Is this sentence singular or plural

Plural
There are two versions of this sentence
A private car is popular.
Private cars are popular.
Your remark is wrong

Given that the module of vector a is 1, the module of vector B is 2, the angle between vector a and B is 60 °, vector C = 2A + 3b, vector D = ka-b (k belongs to R), and vector C is perpendicular to vector D, then the value of K is?
A.-6 B.6 C.-14/5 D.14/5

ab=|a||b|cos60°=2×1/2=1
Because vector C is perpendicular to vector D
So c * d = 0, that is, (2a + 3b) (ka-b) = 0
2ka²+（3k-2）ab-3b²=0
2k+(3k-2)-3×2²=0
The solution is k = 14 / 5
Select [D, 14 / 5]
I wish you a happy study!

How to say "skipping rope" noun and verb in English?

To skip rope
Rope jump

In the triangle ABC, ab = AC, BAC = 120 degrees, points D and F are the midpoint of AB and AC respectively, De is perpendicular to AB, FG is perpendicular to AC, points E and G are on BC, BC = 15
Seeking the length of EG

In △ AMC, AC = 5 √ 3, CF = 5 √ 3 / 2
In △ CGF, CG = 5, BG = 10, eg = 15-5-5 = 5

There is a book on my desk

There are books on my desk