b) \(263^2+74.263+37^2\)

\(=\left(263+37\right)^2\)

\(=300^2\)

\(=90000\)

c) \(136^2-92.136+46^2\)

\(=\left(136-46\right)^2\)

\(=90^2\)

\(=8100\)

cảm ơn lê tài bảo châu nhé

Tính giá trị biểu thức sau:

a, A= \(258^2-\dfrac{242^2}{254^2}-246^2\approx\) 6047,1

b, B= \(263^2+74.263+37^2=90000\)

c, C= \(136^2-92.136+46^2=8100\)

d, D = \(\left(50^2+48^2+46^2+...+2^2\right)-\left(49^2+47^2+45^2+...+1^2\right)\)

= 22100 - 20825= 1275

\(\frac{63^2-47^2}{215^2-105^2}=\)  \(\frac{\left(63-47\right)\left(63+47\right)}{\left(215-105\right)\left(215+105\right)}\)

                           \(=\frac{16.110}{110.320}=\frac{16}{320}\)\(=\frac{1}{20}\)

các câu kia làm tương tự nha

Thanks bạn nhiều nhiều nha!

nhưng câu d với câu e mk khô hiểu lắm!

\(\frac{258^2-242^2}{254^2-246^2}=\frac{\left(258+242\right)\left(258-242\right)}{\left(254+246\right)\left(254-246\right)}=\frac{500.16}{500.8}=2\)

\(263^2+74.263+37^2=263^2+2.37.263+37^2=\left(263+37\right)^2=300^2=90000\)

\(136^2-92.136+46^2=136^2-46.2.136+46^2=\left(136-46\right)^2=90^2=8100\)

\(=\left(50^2-49^2\right)+\left(48^2-47^2\right)+.....+\left(2^2-1^2\right)=\left(50+49\right)\left(50-49\right)+\left(48+47\right)\left(48-47\right)+....+\left(2+1\right)\left(2-1\right)=\left(50+49+....+1\right)=\frac{51.50}{2}=51.25=1275\)

B1: a) \(\left|x-2\right|+9y^2+12xy+4x^2=0\)

=> \(\left|x-2\right|+\left(3y+2x\right)^2=0\)

Ta có: \(\left|x-2\right|\ge0\forall x\)

         \(\left(3y+2x\right)^2\ge0\forall x;y\)

=> \(\left|x-2\right|+\left(3y+2x\right)^2\ge0\forall x;y\)

Dấu "=" xảy ra khi: \(\hept{\begin{cases}x-2=0\\3y+2x=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=2\\3y=-2x\end{cases}}\Leftrightarrow\hept{\begin{cases}x=2\\3y=-2.2=-4\end{cases}}\Leftrightarrow\hept{\begin{cases}x=2\\y=-\frac{4}{3}\end{cases}}\)

Vậy ...

\(A=263^2+74.263+37^2\)

\(=263^2+2.263.37+37^2\)

\(=\left(263+37\right)^2\)

\(=300^2=90000\)

\(B=136^2-92.136+46^2\)

\(=136^2-2.136.46+46^2\)

\(=\left(136-46\right)^2\)

\(=90^2=8100\)