108\(m^2\)

`45%` của `240m^2` là: `240 . 45% = 108 (m^2)`

Gọi `x (x > 0)` là cạnh ban đầu của mảnh đất 

Ta có:

Chiều dài mảnh đất khi mở rộng là `x + 4 (m)`

Chiều rộng mảnh đất khi mở rộng là `x + 3 (m)`

=> Diện tích mảnh đất khi mở rộng là: 

`(x+4)(x+3) = 342`

`<=> x^2 + 7x + 12 = 342`

`<=> x^2 + 7x - 330 = 0`

`<=> (x^2 - 15x) + (22x - 330) = 0`

`<=> x(x-15) + 22(x - 15) = 0`

`<=> (x+22)(x-15) = 0`

`<=> x = -22` (không thỏa mãn) hoặc `x = 15`

Vậy cạnh mảnh đất ban đầu là `15m`

Diện tích mảnh đất lúc đầu là: 

`15 . 15 = 225 (m^2)`

Đáp số: `225m^2`

a: \(15\left(x-15\right)=0\)

mà 15>0

nên x-15=0

=>x=15

c: (x-15)-75=0

=>x-15=75

=>x=75+15=90

b: 32(x-10)=32

=>x-10=1

=>x=10+1=11

d: 575-(6x+70)=445

=>6x+70=575-445=130

=>6x=60

=>x=10

e: 315+(125-x)=435

=>440-x=435

=>x=440-435=5

g: x-105:21=15

=>x-5=15

=>x=15+5=20

h: \(231-\left(x-6\right)=1339:13\)

=>231-(x-6)=103

=>x-6=231-103=128

=>x=128+6=134

i: 70-5(x-3)=45

=>5(x-3)=70-45=25

=>x-3=5

=>x=5+3=8

k: 13-2(x+1)=7

=>2(x+1)=13-7=6

=>x+1=3

=>x=2

i: \(420+65\cdot4=\left(x+175\right):5+30\)

=>\(\dfrac{x+175}{5}=390+65\cdot4=390+260=650\)

=>x+175=3250

=>x=3250-175=3075

l: \(32\cdot15:2=\left(x+70\right):14-40\)

=>\(\left(x+70\right):14-40=16\cdot15=240\)

=>\(\left(x+70\right):14=240+40=280\)

=>\(x+70=14\cdot280=3920\)

=>x=3920-70=3850

m: \(165-\left(35:x+3\right)\cdot19=13\)

=>\(\left(35:x+3\right)\cdot19=165-13=152\)

=>35:x+3=152:19=8

=>35:x=8-3=5

=>x=35:5=7

n: \(1+2+3+4+...+x=528\)

=>\(\dfrac{x\left(x+1\right)}{2}=528\)

=>\(x\left(x+1\right)=528\cdot2=1056\)

=>\(x^2+x-1056=0\)

=>(x-32)(x+31)=0

=>\(\left[{}\begin{matrix}x=32\left(nhận\right)\\x=-31\left(loại\right)\end{matrix}\right.\)

p: \(\left(2x-1\right)+\left(4x-2\right)+...+\left(400x-200\right)=5+10+...+1000\)

=>\(\left(2x-1\right)\left(1+2+...+200\right)=5\left(1+2+...+200\right)\)

=>2x-1=5

=>2x=6

=>x=3

1. I/not/meet/him/before/. Who/he/be?

I haven't met him before. Who is he?

2. He/know/me/ a long time/ but/he/not/know/ my name.

He has known me for a long time but he doesn't know my name  

3. You/do/exercise/ last night? No, I/just/ do.

Did you do exercise last night? No, I have just done

4. It/stop/rain.

It has stopped raining

5. I/ never/see/ such/ beautiful/ view.

I have never see such a beautiful view

6. We/just/ finish/ first term.

We have just finished the first term

7. She/be/pupil/11 years.

She has been a pupil for 11 years

8. Train/just/ leave/she/be/3 minute / late

The train has just left, she is 3 minutes late

9. He/not/ finish/work/yet.

He hasn't finished his work yet

10. I/ already/post/letter/you.

I have already posted a letter for you

11. Why/not/you/do/homework/yet? GCOGPA

Why haven't you done your homework yet? 

12. Tom/find/key/ 2 hours.

Tom has been finding his key for 2 hours

13. He/ smoke/ 20 cigarettes/ a day.

He smokes 20 cigarettes a day

ai trả lời nhanh nhất thì mình tick cho

ko

Sửa đề: Om là phân giác của góc xOz

a: 

Om là phân giác của góc xOz

=>\(\widehat{xOm}=\widehat{zOm}=\dfrac{\widehat{xOy}}{2}=\dfrac{60^0}{2}=30^0\)

b: Ta có: \(\widehat{xOz}+\widehat{yOz}=180^0\)(hai góc kề bù)

=>\(\widehat{yOz}+60^0=180^0\)

=>\(\widehat{yOz}=120^0\)

On là phân giác của góc yOz

=>\(\widehat{yOn}=\widehat{zOn}=\dfrac{\widehat{yOz}}{2}=\dfrac{120^0}{2}=60^0\)

c: \(\widehat{mOn}=\widehat{mOz}+\widehat{nOz}=60^0+30^0=90^0\)

Do \(\widehat{xOy}\) là góc bẹt =>  \(\widehat{xOy}\) = 180^o

a) Do `Om` là tia phân giác của \(\widehat{xOz}\)

=> \(\widehat{xOm}=\widehat{mOz}=\dfrac{1}{2}\widehat{xOz}=\dfrac{1}{2}.60^o=30^o\)

b) Ta có: \(\widehat{zOy}=\widehat{xOy}-\widehat{xOz}=180^o-60^o=120^o\)

Do `On` là tia phân giác của \(\widehat{yOz}\)

=> \(\widehat{zOn}=\widehat{nOy}=\dfrac{1}{2}\widehat{yOz}=\dfrac{1}{2}.120^o=60^o\)

c) \(\widehat{mOn}=\widehat{mOz}+\widehat{zOn}=30^o+60^o=90^o\)