1 + 3 = the square of 4 = 2. 1 + 3 + 5 + 7 + 11. 19 + 20 = ()

1 + 3 = the square of 4 = 2. 1 + 3 + 5 + 7 + 11. 19 + 20 = ()

1+3+5+…… +19 + 21 = 121 = 11 square

12 (x + y) square + 11 (X-Y) + 2 (X-Y) square=

12(x+y)²+11(x²-y²)+2(x-y)²
=12(x+y)²+11(x+y)(x-y)+2(x-y)²
=[3(x+y)+2(x-y)][4(x+y)+(x-y)]
=(3x+3y+2x-2y)(4x+4y+x-y)
=(5x+y)(5x+3y)

The square of x = 12. X = several

Root 12

As shown in the figure, in ladder ABCD, ad ‖ BC, angle B + angle c = 90? F are AD.BC Try to prove that EF =（

If e is used as eg parallel AB, eh parallel DC, we can get the angle of EGH = ∠ B, EHG = ∠ C, B angle c = 90 degrees, so ∠ EGH ∠ EHG = 90. It is easy to prove that abge and ehcd are parallelograms, and get AE = BG = ed = CH, BF = CF, so FG = FH, so EF = 1 / 2GH = 1 / 2 (BC-AD) in RT triangle EGH

25% of the total coal was used for the first time, 60 tons for the second time, and 1 / 3 of the total coal is left. How many tons of coal is left?

This pile of coal is left = 60 ^ (1-25% - 1 / 3) × 1 / 3 = 60 ^ 12 / 5 × 1 / 3 = 144 × 1 / 3 = 48 tons ~ I'll always answer 523 for you. I wish you progress in your study ~ ~ ~ if you agree with my answer, please click the [adopt as satisfactory answer] button in time ~ ~ the mobile phone questioner comments "satisfied" on the client

All formulas of mean inequality

Car a carries 25% more goods than car B, which means car B carries less goods than car a ()

0.25 / 1.25 equals 20%

1. If a + b > 0 and a ≠ B, compare the size of A3 + B3 and A2B + AB2
2. Solve the inequality about X: a (AX-1) + 2 ＞ 4x
3. Given - 1 ≤ a + B ≤ 1,1 ≤ a-2b ≤ 3, find the value range of 3 + 3B

A and B two cars, at the same time from AB two opposite, meet at 5 kilometers from the midpoint, known a car speed is 6 / 7 of B car speed, find ab

What is the distance between the two places
5÷【1/2-6/（6+7）】
=5÷【1/2-6/13】
=5÷1/26
=130 km

Given the vector a = (1,0), the vector b = (1,1) and the value of X, a + XB is perpendicular to a

Vector a = (1,0), vector b = (1,1)
a+xb=(1,0)+(x,x)=(1+x,x)
If a + XB is perpendicular to a
Then (a + XB) ● a = 1 + X + 0 * x = 0
∴x=-1
When x = - 1, a + XB is perpendicular to a