What is 99 + 100 + 101 + 102 +... + 998 + 999,

What is 99 + 100 + 101 + 102 +... + 998 + 999,

Equal to 450 * (99 + 998) + 999
It's 494649

999 * 99 + 999 simple operation

999*(99+1)=99900

What is (1-2-3 -... - 998) (2 + 3 + 4 +... + 999) - (1-2-3 -... - 999) (2 + 3 + 4 +... + 998)?

Let a = 2 + 3 + 4 + +998
Original formula = (1-A) (a + 999) - (1-a-999) a
=（1-a）（a+999）+a(a+998）
=999

Simple calculation: 4 / 11 × 3 / 5 + 8 / 11 × 4 / 5 and 998 × 998 / 999

(4/11)×(3/5)+(8/11)×(4/5)
Here's how it works: before the plus sign
Multiplication of denominators
Molecular multiplication
Turn into the same denominator 55
The sum of the molecules is 44
Final answer = 4 / 5
(999-1)×998/999
=998-(998/999)
=997+1-(998/999)
=997 and 1 / 999

What day is labor day in 2011?

Labor Day in 2011 is Sunday

The function relationship between the braking distance s (m) and the speed V (km / h) of a car is s = V ^ 2 / 100. The speed of a car is 100km / h, which is in front of the car
The functional relationship between the braking distance s (m) and the speed V (km / h) is s = V ^ 2 / 100. A faulty car is found 80 m in front of a car with a speed of 100 km / h. is it dangerous to brake at this time? (please write down the process of the solution)

Vt=V0+at
0=8+a*1
a=-8
S=V0t+1/2at^2
S=8*1+1/2*(-8)*1*1
S=4m
Less than 5.9m, meeting the requirements

In RT △ ABC, C = 90 ° and cosa = 2 / 3, what is the tanb?

sinB=cosA=2/3
cosB=sqrt(1-(2/3)^)=sqrt(5)/3
tanB=sinB/cosB=2sqrt(5)/5

It takes 10 hours for car a to complete the whole journey. How many hours does it take for car B to complete the whole journey?

35 △ 16-110, = 35 △ 115, = 35 × 15, = 9 (hours); a: it takes 9 hours for car B to complete the whole journey

Given a ^ 2 + B ^ 2-4a + 6B = negative 13, calculate the value of A.B

a²+b²-4a+6b=-13
(a²-4a+4)+(b²+6b+9)=0
(a-2)²+(b+3)²=0
∴{a-2=0
b+3=0
∴a=2,b=-3

The motorcycle wheels rotate rapidly and look like a whole plane, which shows that______ ．

A wheel is like a round surface, which is formed by rotation of an axis. This axis is regarded as a line