Cho tam giác nhọn ABC có BC = 13 cm , CA = 14 cm , AB = 15 cm .

Tính a : cosA , sinA

b : \(S_{ABC}\)

Tính số đo góc nhọn x biết

a , tanx = cotgx

b , \(2sin^2x+3cos^2x=\dfrac{9}{4}\)

cho tam giác ABC có BC = a , AC = b , AB = c , Các đường trung tuyến BM và CN vuông góc với nhau .

a . Tính a theo b và c .

b . CMR \(cotgB+cotgC\ge\dfrac{2}{3}\)

CMR trong 1 tam giác nhọn bình phương 1 cạnh bằng tổng bình phương 2 cạnh còn lại trừ 2 lần tích 2 cạnh với cos góc xen giữa 2 cạnh ấy : \(a^2=b^2+c^2-2bc.cosa\)

fill in each blank with a suitable word forn the list .

friendship , understanding , know , subjects , written , what , many , to

English is a very useful language . If we ...................... ( 1 ) english , we can go to any countries we like . We will not find it hard to make people understand ......................... ( 2 ) we want to say . english also helps us to learn all kinds of ................... ( 3) . Hundreds of books are .................. ( 4 ) in English everyday in ................................. ( 5 ) countries . English has also helped to spread ideas and knowledge .......................... ( 6 ) all corners of the world . Therefore , the English language has helped to spread better ............................... ( 7 ) and ................................. ( 8 ) among countries of the world .

besides in - class assignments , our teacher often gives some ......................... for us to do at home .

a , housework

b , homework

c , teamwork

d , classwork

rewrite the following sentences .

1 / study hard and you will pass the exam .

- if .....................................................................

2 , save some money or you won't able to buy the house .

- if ...........................................................................

3 , be good or your parents will be very unhappy .

- if .............................................................................

4 , do it carefully or you will feel sorry afterwards .

- if ......................................................................................

5 , ask him first and he will offer to help .

- if ..................................................................................

6 , be calm or you will make a wrong decision .

- if ......................................................................................

7 , be careful or you will cut yourself with that knife .

- if ...................................................................................