my mother suggested preparing food carefully before turning on the stove

->my mother suggested that

he is the best guitar player in the group

->nobody

It's useful to get access to the tnternet

->Getting

It's very useful to speak English fluently

->Speaking

My mother bought me a new bike yesterday

->A new bike

She feelscomfortable to watch T.V

->Watching T.V

She bought that television 2 weeks ago

->She has

It took me a fairy long time to answer all may e-mails

I spent

Mr.Peter fixed the sewing machine for my mother

-> My mother got

The flight from HN city to HCM city takes 3 hours

->It takes

Cho hình chữ nhật ABCD, AB=2BC.TRên cạnh BC lấy điểm E, tia AE cắt CD tại F, vẽ AK\(\perp\)AF(K\(\in\)CD):

CMR:\(\dfrac{1}{AB^2}=\dfrac{1}{AE^2}+\dfrac{1}{4AF^2}\)

Cho \(\Delta\)ABC cân tại A, dường cao Ah và BK. Qua B kẻ đương thẳng vuông góc với BC cắt tia đối của tia AC tại D. CMR:

a)BD=2AH

b)\(\dfrac{1}{BK^2}=\dfrac{1}{BC^2}+\dfrac{1}{4AH^2}\)

Cho \(\Delta\)ABC vuông tại A, đường cao AH.CMR: \(BC^2=2AH^2+BH^2+CH^2\)

"How many people are there in your family?"She asked John