`x+y+z=0`
`⇔(x+y+z)^2=0`
`⇔x^2+y^2+z^2+2xy+2yz+2zx=0`
`⇔x^2+y^2+z^2=-2(xy+yz+zx)`
Ta có:
`(9(x^2+y^2+z^2))/((x-y)^2+(y-z)^2+(z-x)^2)`
`=(9(x^2+y^2+z^2))/(x^2-2xy+y^2+y^2-2yz+z^2+z^2-2xz+x^2)`
`=(9(x^2+y^2+z^2))/(2(x^2+y^2+z^2)-2(xy+yz+zx))`
`=(9(x^2+y^2+z^2))/(2(x^2+y^2+z^2)+x^2+y^2+z^2)`
`=(9(x^2+y^2+z^2))/(3(x^2+y^2+z^2))`
`=3`
Giải thích các bước giải:
\(\begin{array}{l}x + y + z = 0\\ \Leftrightarrow {\left( {x + y + z} \right)^2} = 0\\ \Leftrightarrow {x^2} + {y^2} + {z^2} + 2xy + 2yz + 2zx = 0\\ \Leftrightarrow {x^2} + {y^2} + {z^2} = - 2.\left( {xy + yz + zx} \right)\\\dfrac{{9\left( {{x^2} + {y^2} + {z^2}} \right)}}{{{{\left( {x - y} \right)}^2} + {{\left( {y - z} \right)}^2} + {{\left( {z - x} \right)}^2}}}\\ = \dfrac{{9\left( {{x^2} + {y^2} + {z^2}} \right)}}{{\left( {{x^2} - 2xy + {y^2}} \right) + \left( {{y^2} - 2yz + {z^2}} \right) + \left( {{z^2} - 2zx + {x^2}} \right)}}\\ = \dfrac{{9\left( {{x^2} + {y^2} + {z^2}} \right)}}{{2\left( {{x^2} + {y^2} + {z^2}} \right) - 2.\left( {xy + yz + zx} \right)}}\\ = \dfrac{{9\left( {{x^2} + {y^2} + {z^2}} \right)}}{{2\left( {{x^2} + {y^2} + {z^2}} \right) + \left( {{x^2} + {y^2} + {z^2}} \right)}}\\ = \dfrac{{9\left( {{x^2} + {y^2} + {z^2}} \right)}}{{3\left( {{x^2} + {y^2} + {z^2}} \right)}} = 3\end{array}\)
7. The villagers / try/ learn English/ order/ they/communicate /foreigners. ………………………………………………………………………………………………………. 8. Where / you/find /about/Disneyland Resort ? ……………………………………………………………………………………………………… 9. though/hand-embroidered/ picture/expensive/ we/ bought. ………………………………………………………………………………………………… 10. What time/you/out of /bed/ this morning? ………………………………………………………………………………………….. giúp em với cho em cảm ơn trước
Nêu cách sử dụng thì hiện tại hoàn thành ?
Mong các bạn giúp mình đang cần gấp
vẽ cho mình Kun (TTK) đang nấu ăn nha ! và nhớ là có màu nhá ! ^^
vẽ, digi, tradi gì cx đc miễn vẽ đẹp cho mk là đc vẽ 1 trong 2 nha cả 2 càng tốt
Đổi các câu sau thành câu bị động Từ câu 14-29
complete the sentences with a verb the past continuous. example : I was eating dinner, so i didn't answer the phone( eat) 1. i took this photo when my wife ................ in the yard (work) 2. He met his wife when he ............. in Japan (live) 3. they ............. for us when we arrived ( Not wait) 4. ............ she .............. a coat when she went out ? ( wear) 5. The sun .............. when i left for work. ( shine) 6. What ....... you ............ at 7:30 last night ? (do) 7. I ............... when you gave the instructions. ( no listen ) 8. we ............. TV when you called ( not watch ) hứa cho 5 sao lun (^-^)!!!
Vẽ anime cặp ......................
56.They chose Philip to be chairperson. (MADE) Philip ___________________________________________________________________________ 57. “It was me who broke the valuable vase,” Tim said apologetically. (ADMITTED) Tim apologetically ________________________________________________________________ 58. Passengers should fasten their seatbelts during the take-off. Passengers are ___________________________________________________________________ 59. “You shouldn’t walk alone in dimly lit streets late at night, Jane”, said her father. (AGAINST) Jane’s father _____________________________________________________________________ 60. If someone gave you a free airline ticket, where would you travel to? (TO) If you ___________________________________________________, where would you travel to? 61. I don’t like it when you lied to your parents about the event. (RATHER) I ______________________________________________________ your parents about the event. 62. It’s a pity that you forgot to phone your mum last week. (SHOULD) You ___________________________________________________________________________
Cứu với ...............,,.......,
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