Choose between for and since for each of the following questions. 1. I've known my best friend 15 years.
a) for
b) since
2. last Christmas, I haven't eaten any chocolate.
a)for
b)since
3. He's been sick the last week.
a)for
b)since
4. Bob's worked there 1984.
a) for
b) since
5. I've been telling you to hurry up the last 30 minutes!
a)for
b)since
6. My mother has been trying to call me last week.
a) for
b) since
7. They have been colleagues a long time.
a)for
b)since
8. He has been studying Russian a few months.
a) for
b)since
9. I haven't seen her last year.
a)for
b) since
10. I've been angry at him a couple of weeks ago.
a) for
b)since
Внешний угол треугольника равен сумме двух внутренних, не смежных с ним.
1) Внешний угол треугольника 100°:
∠С + ∠В = 100°
∠C = 100° - ∠B = 100° - 48° = 52°
∠BCA = 52°
2) Внешний угол ∠ABD = ∠С + ∠A = 90° + 46° = 136°
Внешний угол при вершине другого острого угла 136°
3)В равнобедренном треугольнике углы при основании равны.
Внешний угол 140°: ∠A + ∠C = 140°
2∠A = 140° ⇒ ∠A = 140°/2 = 70°
Угол при основании равен 70°
4) Пусть Х = ∠CBK - внешний угол при вершине В,
тогда Х + 64° - внешний угол при вершине А
∠CВA = 180°- Х - смежные углы
∠CAD - по правилу внешнего угла:
∠CAD = ∠C + ∠CBA
X + 64° = 80° + (180° - X)
2X = 196° ⇒ X = 196°/2 = 98°
∠B = ∠CBA = 180°- X = 180° - 98° = 82°
∠B = 82°