A = 2, CoSb = 3 / 5, C = 45 ° to find the area of triangle ABC Solving problems with cosine theorem

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• 1. In triangle ABC, angle a = 108 degrees, angle c-angle B = 28 degrees, then angle C=
• 2. It is known that ABC is the length of three sides of a triangle. Try to compare the size of a square + b square + C square and 2BC
• 3. In the triangle ABC, if the lengths of three sides are a, B and C respectively, and the square of a + 2Ab = the square of C + 2BC, then the triangle ABC is a triangle
• 4. In the triangle ABC, a, B and C are the opposite sides of ∠ a, B and C respectively. Try to compare the square of a-b-c and the square of 2BC
• 5. If a, B and C are the three sides of triangle ABC, and 3 (a square + b square + C Square) = (a + B + C) square, judge the shape of triangle ABC?
• 6. In triangle ABC, if angle a + angle B = 2 angle c, angle a-angle C = 40 °, what triangle is it?
• 7. Send a 5-inch, 5.3-inch, 5.5-inch, 6-inch mobile phone comparison chart? I really don't know what size is
• 8. As shown in the figure, it is known that ∠ 1 + 2 = 180 ° and ∠ 3 = B. try to judge the relationship between ∠ AED and ∠ C, and rationalize the conclusion
• 9. Figure 1 is 9cm in length and 6cm in width, figure 2 is 3cm in length and figure 3 is 12cm in width
• 10. A gymnasium inlays the floor with rectangular wood blocks of the same size, and paves two blocks for the first time, as shown in Figure 1. The second time completely encloses the first time, as shown in Figure 2 and figure 3 The second paving is completely enclosed, as shown in Figure 3. In this way, after the nth paving, the letter N is used to indicate the number of wood blocks used in the nth figure
• 11. In △ ABC, a = 7, B = 43, C = 13, then the minimum angle is () A. π3B. π6C. π4D. π12
• 12. Three years ago, my father's age was five times that of Xiaoli. Five years later, my father's age is three times that of Xiaoli. How old is Xiaoli this year? I want the process of arithmetic! Besides, I don't know the quadratic equation of two variables!
• 13. Cut a cube with an edge length of 8 cm into two cuboids. What is the total surface area of the two cuboids?
• 14. What is the surface area of a cuboid made up of a square with three edges 8 cm long?
• 15. Divide a square with an edge length of 8 cm into two rectangles of the same size and shape. What is the surface area of each rectangle Such as the title One l
• 16. Four edges are 8 cm long square, put together into a rectangle, what is the surface area
• 17. How many square centimetres is the surface area of a rectangle made of 3 squares with 8 cm edges?
• 18. Xiao Li uses a rectangular piece of paper with a length width ratio of 3:2 and an area of 420cm to cut a square piece of paper with an area of 324 square centimeters along the direction of the edge. You can help Xiao Li calculate. Can she use a large piece of paper to cut a small piece of paper?
• 19. Xiao Li wants to cut a rectangular piece of paper with an area of 30 square centimeters on a square piece of paper with an integer length, and make its length and width 2:1. Question: how long is the side length of Xiao Li's square piece of paper at least?
• 20. Xiao Li wants to use a square piece of paper with an area of 400 square centimeter to cut a rectangular piece of paper with an area of 300 square centimeter along the direction of the side, so that its length width ratio is 3:2. I don't know if it can be cut out, but she is worried. Xiao Ming said, "don't worry, you can cut a small piece of paper with a large piece of paper." do you agree with Xiao Ming? Please give reasons