Question

tính nhanh

\(a,\left(31,8\right)^2-2.31,8.21,8+\left(21,8\right)^2\)

\(b,\left(7,5\right)^2+2.7,5.2,5+\left(2,5\right)^2\)

giúp mình nhé mình đang cần gấp

Answer 1

Giải:

a) \(\left(31,8\right)^2-2.31,8.21,8+\left(21,8\right)^2\)

\(=\left(31,8-21,8\right)^2\)

\(=10^2=100\)

Vậy ...

b) \(\left(7,5\right)^2+2.7,5.2,5+\left(2,5\right)^2\)

\(=\left(7,5+2,5\right)^2\)

\(=10^2=100\)

Vậy ...

HĐT: \(\left(A\pm B\right)^2=A^2\pm2.A.B+B^2\)

Answer 2

a, (31,8)² - 2.31,8.21,8+(21,8)²

=(31,8+21,8)² =10² =100

b,(7,5)² + 2.7,5.2,5 +(2,5)²

=(7,5 +2,5)² =10² =100