a) Ta có: góc ATx kề bù với góc ATH nên:

góc ATx+góc ATH=90^o

=>góc ATx=90^o-góc ATH=90^o-40^o=50^o

b)thiếu đề

a) ax^2-bx^2+bx-ax+a-b

=(ax²-bx²)+(bx-ax)+(a-b)

=x².(a-b)-x.(a-b)+(a-b)

=(a-b)(x²-x+1)

b) 2a^2+4a+2

=2a²+2a+2a+2

=2a.(a+1)+2.(a+1)

=2.(a+1)(a+1)

12 con chuột 

tich mình nha

3 con mèo ăn trong 6 giờ được:

                   3.(6:3)=6(con)

=>6 con mèo ăn trong 6 giờ được:

                   6.(6:3)=12(con)

\(\frac{a}{b}:\frac{c}{d}=\frac{a}{b}.\frac{c}{d}\Rightarrow\frac{a}{b}=\frac{a}{b}.\frac{c}{d}.\frac{c}{d}\Rightarrow\frac{a}{b}:\frac{a}{b}=\frac{c}{d}.\frac{c}{d}\)

\(\Rightarrow1=\left(\frac{c}{d}\right)^2\Rightarrow\frac{c}{d}=1\text{ hoặc }\frac{c}{d}=-1\)

\(\frac{1}{1.2}+\frac{1}{3.4}+...+\frac{1}{49.50}=1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}=\left(1+\frac{1}{3}+\frac{1}{5}+...+\frac{1}{49}\right)-\left(\frac{1}{2}+\frac{1}{4}+...+\frac{1}{50}\right)\)

\(=\left(1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{50}\right)-2\left(\frac{1}{2}+\frac{1}{4}+...+\frac{1}{50}\right)\)

\(=\left(1+\frac{1}{2}+..+\frac{1}{50}\right)-\left(1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{25}\right)=\frac{1}{26}+\frac{1}{27}+...+\frac{1}{50}\)