If the length of a rectangular cardboard is reduced by 3cm, it will become a square. The area of the square is 21cm less than that of the original rectangle. Do you know the original area of the rectangular board?

If the length of a rectangular cardboard is reduced by 3cm, it will become a square. The area of the square is 21cm less than that of the original rectangle. Do you know the original area of the rectangular board?

Width = 21 / 3 = 7 cm
Length 7 + 3 = 10 cm
Area = 10 * 7 = 70

The maximum value of a sinusoidal alternating current is 100 Ma, the frequency is 50 Hz, and the initial phase angle is zero
Such as the title

The formula is v = Vmax * sin (2 * pi * f * t). If the direction of current is not considered, the answer is 1.66667 Ms. if the direction of current is considered, there are two solutions. One solution is that the current rises to positive 50 Ma after zero, which is about 1.66667 Ms. the other solution is that the current drops after zero, and then returns to zero, which is about 11.667 Ms

Make a rectangular oil tank with iron sheet. The bottom surface is a square with a side length of 50 cm and a height of 80 cm. At least how much iron sheet and how many square centimeters should be used,

A touch of bitterness,
Bottom area: 50 × 50 = 2500 (square centimeter)
Side area: 50 × 4 × 80 = 16000 (square centimeter)
Iron sheet: 2500 × 2 + 16000 = 21000 (square centimeter)

Workload = (), (?) 10008; (). Working hours = () / (). Working efficiency = () / ()
Quick, quick

Total amount of work = (work efficiency) & # 10008; (working hours)
Working hours = (total amount of work) / (working efficiency)
Work efficiency = (total amount of work) / (working hours)

The surface area and volume of the cone are calculated by taking the sector with the center angle of 120 ° and the area of 3 π as the side of the cone

Let the generatrix of the cone be l, the radius of the bottom surface be r, ∵ 3 π = 13 π L2 ∵ L = 3, ∵ 120 ° = R3 × 360 °, ∵ r = 1, ∵ the height of the cone is 9-1 = 22 ∵ the surface area of the cone is π R2 + π RL = 4 π, and the volume of the cone is 13 × π × 12 × 22 = 22 π 3

Check the division of the remainder, you can use what and what product plus what equals to check

Product plus remainder of multiple

The perimeter ratio of the big and small circles is 6:5. The area of the big circle is 72 square decimeters. What is the area of the small circle

The area of the great circle is s = π × R & # 178; = π × (C △ π △ 2) &# 178;
The area of small circle is s = π × R & # 178; = π × (C △ π △ 2) &# 178;
The area ratio of large and small circles is s: S = C & # 178;: C & # 178;, that is 36:25
Therefore, the area of small circle is 72 × 25 / 36 = 50 (square decimeter)

In the pyramid s-abcd, the bottom surface ABCD is a square, SA is a vertical plane ABCD, SA = AB, e is the midpoint of AB, f is the midpoint of SC

AB-S --S -SADA -S-D --AD- QW-D- --ASD -QDAW- W-DA- D D AD*QWD -QD-A- -QD-Q-+ QWE- --D-A DAWD Q

When a set of data is like this, what is the degree of the sector graph?
Number of people 4 15 25 5
They were 13 years old, 14 years old, 15 years old and 16 years old

4 + 15 + 25 + 5 = 494 / 49 = 8.16%, 8.16% * 360 = 2915 / 49 = 30.61%, 30.61% * 360 = 11025 / 49 = 51.02%, 51.02% * 360 = 1845 / 49 = 10.20%, 10.20% * 360 = 37, age 13, 14, 15, 16 years old, respectively, accounting for 29110, 184, 37

Given that the second, third and sixth terms of an arithmetic sequence with nonzero tolerance are three consecutive terms of an arithmetic sequence, then the common ratio of the arithmetic sequence is equal to ()
A. 34B. −13C. 13D. 3

∵ the second, third, and sixth items of the arithmetic sequence with non-zero tolerance are three consecutive items of an arithmetic sequence in turn, ∵ (a1 + 2D) 2 = (a1 + D) (a1 + 5d). After sorting out, we get A1 & nbsp; = − D2. ∵ the common ratio of this arithmetic sequence is q = a1 + 2da1 + D = − D2 + 2D − D2 + D = 3