Tuổi của mẹ là :

2 : ( 1/4 - 1/5 ) = 40 ( tuổi )

Đáp số : 40 tuổi

Gọi 2 số cần tìm là a và b

\(\Rightarrow\frac{a}{b}=\frac{5}{7}\)

\(\Rightarrow\frac{a}{5}=\frac{b}{7}\)

\(\Rightarrow\frac{a^2}{25}=\frac{b^2}{49}\)

Mặt khác

\(a^2+b^2=4736\)

Áp dụng tc của dãy tỉ số bằng nhau Ta có

\(\frac{a^2}{25}=\frac{b^2}{49}=\frac{a^2+b^2}{25+49}=\frac{4736}{74}=64\)

\(\Rightarrow\begin{cases}a=\pm40\\b=\pm56\end{cases}\)

Mà 5.7>0

=> \(a.b\ge0\)

\(\Rightarrow\left(a;b\right)=\left\{\left(40;56\right);\left(-40;-56\right)\right\}\)

\(\left(2x-5\right)\left(x-3\right)=2x^2+2004\)

\(\Rightarrow2x^2-6x-5x+15=2x^2+2004\)

\(\Rightarrow\left(2x^2-2x^2\right)-\left(6x+5x\right)=2004-15\)

\(\Rightarrow-11x=1989\)

\(\Rightarrow x=-\frac{1989}{11}\)

\(\Rightarrow\left(2+7+....+47\right)+10x=665\)

\(\Rightarrow\frac{\left(47+2\right)10}{2}+10x=665\)

\(\Rightarrow245+10x=665\)

\(\Rightarrow10x=420\)

\(\Rightarrow x=42\)

Đường chéo chiếc TV dài

\(2,45.21=51,45\left(cm\right)\)

Vậy đường chéo chiếc TV dài 51 , 45 cm

Gọi tia đói của Ax là Ax'

a)

Ta có

\(\widehat{xBz}=\widehat{xAy}=50^0\) ( Hai góc đồng vj ; Bz // Ay )

b)

\(\widehat{BAy}=\widehat{x'Bz}\)( đồng vị )

Mặt khác

\(\widehat{A1}=\frac{1}{2}.\widehat{BAy}\)

\(\widehat{B1}=\frac{1}{2}.\widehat{x'Bz}\)

\(\Rightarrow\widehat{A1}=\widehat{B1}\)

MÀ \(\widehat{A1};\widehat{B1}\) đồng vị

=> Am//Bn

a)

\(495\approx500\)

\(52\approx50\)

\(\Rightarrow495.52\approx500.50=25000\)

b)

\(82,36\approx80\)

\(5,1\approx5\)

\(\Rightarrow82,36.5,1\approx80.5=400\)

c)

\(6730\approx7000\)

\(48\approx50\)

\(\Rightarrow6730:48\approx7000:50=140\)

1. My father gave up smoking two years ago. He ______used to smoke________ (smoke) a packet of cigarettes a day.
2. There_____used to be______________ (be) a movie theater here but it closed a long time ago.
3. Mr. An________did not use to drink___________ (not drink) coffee when he was young but he like it now.
4. Peter_______used to have____________ (have) a motorbike, but last month he sold it and bought a car.
5. I________did not use to like___________ (not like) her but we are best friends now.
6.They came to live in the city last year. They______used to live_____________ (live) in a small village in the country.
7. My sister ________used to play___________ (play) tennis a lot but she doesn’t play very often now.
8. When I was a child I__________did not use to study_________ (not study) hard.

1. be => was / were

2. find => found 

3. use => used

4. fall => fell

5. light => lit / lighted

6. escape  =>  escaped

 7. make => made

8. graze => grazed

9 , fit => fitted

10. lose=> lost

11. go  => went

12. choose=> chose

13. appear => appeared

14. come => came

15. hold => held

16. break  => broke