1. We need to decide how to celebrate your birthday,
2 You needn't to go to the shop. I have bought everything we need.
3. Pupils must wear uniforms at school. It's a rule!
4. They don't have to cook dinner. Mother has done it.
5. People mustn't cross the street when traffic lights are red!
6. You have to do morning exercises! It's very useful!
7. May I take your pen? I have lost my pen
8. My friend can't speak English, but he speaks French.
9. You shouldn't go out if you feel not very well.
10. I should to take my umbrella, it's raining
Объяснение:
the side surface of this pyramid consists of 6 isosceles triangles with a base 16 and a side 17.
Find the area of one triangle.
S = 1/2bh, where b is the base and h is the height.
The height is found by the Pythagorean theorem.
The height is equal to the square root of the difference between the squares of the side of the triangle and the half of the base. Half of the base 16 / 2 = 8
17*17 - 8*8 = 225. The square root of 225 is 15. The height of the triangle is 15. Then the area of the triangle will be equal to S = 1/2*16*15 = 120 and the area of the side surface of this pyramid is equal to the area of one triangle multiplied by 6. S1 = 120 * 6 = 720