1. She was surprised when she found a golden coin in the garden.

2. I will go shopping right after as soon as I find my wallet.

3. Before he made a quick phone call to a client, he left the office.

4. He took a rest after he mowed the lawn.

a/ \(x^2+25-10x\)                  b/ \(-8y^3+x^3\)

= \(x^2-10x+25\)                     = \(x^3-8y^3\)

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

= \(\left(x-5\right)^2\)                              = \(\left(x-2y\right)\left[x^2+x.2y+\left(2y\right)^2\right]\)

                                              = \(\left(x-2y\right)\left(x^2+2xy+4y^2\right)\)

Cu(OH)₂: Copper (II) hydroxide

N₂O: Nitrogen (I) oxide

BaSO₄: Barium sulfate

H₂S: Hydrogen sulfide

A = {x|xϵ N và x ≤ 7}

A = {0, 1, 2, 3, 4, 5, 6, 7}

B = {x|xϵƯ(21) và x > 0}

B = {1, 3, 7, 21}

=>  A ∩ B = {1, 3, 7}

Dear Lily,

I'm happy to hear that you’re going to join the Ok Om Bok Festival next week. Here, I have some advice for you on what to do and avoid doing at the festival.

First, you should dress properly, and don’t forget to wear comfortable shoes because you may walk a lot. Second, you should be quiet when the monks and the elders are talking. Last but not least, always show respect to the monks and the elders.

Also, I should remind you that you mustn’t litter on the ground or climb on the statues in the temple. Besides, you shouldn’t refuse young rice when the elders offer it to you. Anyway, I hope you will have a great time.

Best wishes,

Things I do to help my family:

+ herd cattle

+ feeding pigs, dogs and cat.

+ look after the house.

+ cook meal

+ catching fish

1+2+3+4+...+49+50

=\(\dfrac{\left(1+50\right)\cdot50}{2}\) 

=\(\dfrac{51.50}{2}\) 

=\(\dfrac{2550}{2}\)

=\(1275\)