Точка H — ортоцентр треугольника ABC, R — радиус окружности, описанной около этого треугольника. Докажите, что AH = 2R|cos A|.

He has worked at school since 1997.
They rose when the teacher came in.
He has already grown up.
When she fell, she was immediately helped to get up.
This term I've learnt a lot of new words.
His team won the last match, but had lost the match before.
He shook his son on the shoulders.
She threw all the rubbish away as soon as she came back.
They haven't written about their holiday yet.
What's she singing? I've never heard that song before.
We were drinking tea and talking when the phone rang.
When did he see his mistake? He only saw it when I told him about it.
If you come at 8 tomorrow, we will be talking about your job.
I would be glad if you could help me.
I'm sure I will have passed all exams by July.
Are you going anywhere this summer?