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How to use letters to represent numbers in the second volume of grade four?
For example, if a car travels 70 kilometers per hour, how many hours does it take for the car to travel 350 kilometers? This question is very simple, that is, 350÷70=5 (hours).

The car travels one kilometer per hour, so how many hours does it take for the car to travel b kilometers? In fact, as long as we understand the relationship between distance, speed and time, this problem can be easily solved.

Distance = speed × time, time = distance/speed. In this topic, distance and speed are known, and time can be found by using the formula, and time = b ÷ a, what children don't understand is why this formula can't be solved.

The length of side a of the extended data square is c = 4as = a2.

Rectangle a- length b- width c = 2 (a+b) or c = 2a+2bs = ab.

Triangle a-height S= ah or S=ah÷2 or S= on the bottom h-a.

Trapezoidal s = (a+b) h/a- upper bottom b- lower bottom h- height S =(a+b)h or S=(a+b)h÷2.

radius of a circle

C =πd = 2πr- radius d- diameter

π-πC =πd or c = 2π rs C=2πr S=πr2.

D= or d=c÷ π

R= or r=c÷π÷2

Ring r- excircle radius

S =π(R2-R2)r- radius of inner circle

R- outer circle radius ring = outer s- inner s = π (R2-R2)

Stereographic figure

The letter of the graphic name indicates s- region v- volume.

A side length of cube = 12a S table = 6a2s base = A2