ét ô ét :))

1) Fred.......................(answer) the phone if his wife (have) a bath.
2) If Claire....................(wear) this dress at the party, our guests...................................(not stay) any longer.
3) If I..............(touch) this snake, my girlfriend.................(not scream).
4) She............(forget) to pick you up if you (not phone) ………….her.
5) I....................(remember) you if you.....................(give) me a photo.

1) If we...................(send) an invitation, our friends.................(to come) to our party.
2) He.................(not understand) you if you (whisper)……………..
3) They.......................(not survive) in the desert if they.........................(not take) extra water with them.
4) If you................(Press) CTRL + s, you.....................(save) the file.
5) You......................(cross) the Channel if you................(fly) from Paris to London

chứng minh rằng 

A= x²-x+1>0,∀x

B= x²+x+1>0,∀x

C= x²+2x+2>0,∀x

tìm GTLN của biểu thức 

A=12x-3x²

B=2x-2xy-2x²-y²

C= -4x²-12x