Please teachers, brothers and sisters, 1. Use a 12.4 decimeter long wire to form an isosceles trapezoid. The two waists are 6.4 decimeters long, and the area is 9 square decimeters. 2. A barrel of oil weighs 9.2 kg. After half pouring, the barrel weighs 5.6 kg. How many kg? 3. The school bought 4 desks and 9 chairs for 891 yuan. It is known that the price of one desk and 6 chairs is the same, How much is a desk? (equation) 4. For two barrels of oil, the weight of a is 1.8 times that of B. If 1.2kg is taken out of a barrel, then the weight of the two barrels of oil is equal. How many kg are the two barrels of oil?

Please teachers, brothers and sisters, 1. Use a 12.4 decimeter long wire to form an isosceles trapezoid. The two waists are 6.4 decimeters long, and the area is 9 square decimeters. 2. A barrel of oil weighs 9.2 kg. After half pouring, the barrel weighs 5.6 kg. How many kg? 3. The school bought 4 desks and 9 chairs for 891 yuan. It is known that the price of one desk and 6 chairs is the same, How much is a desk? (equation) 4. For two barrels of oil, the weight of a is 1.8 times that of B. If 1.2kg is taken out of a barrel, then the weight of the two barrels of oil is equal. How many kg are the two barrels of oil?

1. Use a 12.4 decimeter long iron wire to form an isosceles trapezoid. The two waists are 6.4 decimeters long and the area is 9 square decimeters. Find the height of the trapezoid. If there is a problem with the given figure, I will tell you the method: divide the area by 2 times of the iron wire length minus 2 times of the waist length, and the quotient is the height of the trapezoid. 2. The weight of a barrel of oil is 9.2 kg

Three tough math problems I hope you can teach me how to do the problem
1: In trapezoidal ABCD, if ad ‖ BC, ad = 1, BC = 4, ∠ C = 70 ° and ∠ B = 40 °, the length of AB is ()
2: If the length of the upper base of an isosceles trapezoid is equal to the length of the waist, and a diagonal line is perpendicular to the waist, what is the degree of the upper base angle of the trapezoid?
3: In trapezoidal ABCD, ab ‖ CD, ∠ a = 90 °, ab = 2, BC = 3, CD = 1, e is the midpoint of AD
Verification: CE ⊥ be (PS: trapezoid two top angle letters are D, C, bottom angle is a, b)

See the title came in, fortunately, not difficult
1) Extend Ba, CD intersection angle e is 180-40-70 = 70, so be = BC = 4, AE = ad = 1, ab = be-ae = 3
2) Let BDC = x, C = 2x, x + 2x = 90, x = 30, and top bottom angle = 30 + 90 = 120
3) Let CF be vertical AB, CF = root sign (3 Square-1 Square) = 2 root sign 2, de = root sign 2, CE square = 3, be square = 2 + 4 = 6, CE square + be square = BC square