2 (x + 18.3) = 67.8 solution test

2 (x + 18.3) = 67.8 solution test

2（x+18.3)=67.8
x+18.3=67.8/2
x+18.3=33.9
x=33.9-18.3
x=15.6

If the circumference of a semicircle is 10.28 cm, the area of the semicircle is ()

Circumference of semicircle = D + π r = 2R + π r = (2 + π) r = 10.28
Then r = 10.28 / (2 + 3.14) = 10.28/5.14 = 2 (CM)
S = 1 / 2 π R ^ 2 = 1 / 2x3.14x2 ^ 2 = 6.28 (cm2)

12.5 * 1.9-1.25-1.25-1.25 (simple operation)

Original formula = 1.25 * 19-3 * 1.25 = 1.25 * 16 = 1.25 * 8 * 2 = 10 * 2 = 20

As shown in the figure, ab = DC, ad = BC, points E and F are the points on the extension line of AD and CB respectively, and de = BF, prove be = DF,

Proof: connect BD
In Δ abd and Δ CDB
∵ AB = DC ad = BC (known) BD = dB (common side)
∴ΔABD≌ΔCDB(SSS)
∴

There are five permutations A1, A2, A3, A4, A5, among which the different permutations satisfying "AK ≥ K-2 for all k = 1, 2, 3, 4, 5" are______ Species

Now the given permutation must satisfy a condition, that is, AK ≥ K-2, such as A5 ≥ 3, so now A5 can't be all five numbers, it must be greater than or equal to 3, so 1, 2 and other numbers can't work. The specific method is to select A5 first, which can only select 3, 4, 5, and only three possibilities; then select A4, which can select one of the previous three and the remaining two, You can also choose the number 2, so there are still only three possibilities So the permutation number should be 3 × 3 × 3 × 2 × 1 = 2 × 35-2 = 54

The area of a trapezoid is 63 square decimeters, the upper bottom is 3 decimeters, and the lower bottom is 18 decimeters. How many decimeters is the height?

Trapezoid area = (upper bottom + lower bottom) × height ／ 2, height = 63 × 2 ／ (3 + 18) = 6 (decimeter)

If f [2 / x + 1] = lgx, then FX =?

Let 2 / x + 1 = t
The result is x = 2 / (t-1)
Just replace x with T

Paint a classroom, 8 meters long and 6.5 meters wide. Now paint the four walls and roof, deducting the area of doors and windows of 16 square meters
What is the area of the fraction?
Painting area

8×6.5＋6.5×3×2＋8×3×2－16
=52＋39＋48－16
=123 square meters
The result of painting area is an integer

If the point P (1,1) is the midpoint of the chord Mn of circle x2 + y2-6x = 0, then the linear equation of the chord Mn is ()
A. 2x+y-3=0B. x-2y+1=0C. x+2y-3=0D. 2x-y-1=0

X2 + y2-6x = 0 is transformed into the standard equation (x-3) 2 + y2 = 9 ∵ P (1,1) is the midpoint of the chord Mn of the circle (x-3) 2 + y2 = 9, the slope of the line determined by the center of the circle and point P is 1 − 01 − 3 = − 12, the slope of the line where the chord Mn is located is 2, and the equation of the line where the chord Mn is located is Y-1 = 2 (x-1), that is, 2x-y-1 = 0

Two triangles of equal area can certainly be combined into a parallelogram

No!
Two triangles with the base length of 4 and height of 3 and the base length of 2 and height of 6 have the same area, but they cannot be combined into parallelogram