Question

Khai triển hằng đẳng thức
a)(x+y)^2 b)(x-4y)^2 c)(3x+1/3y)^2 d)4x^2-81 e)(xy+5)^2 f)(x-y+z)^2

g)1-9y^2 h)(m-2/3n)^2

Answer 1

a, (x+y)² = x² + 2xy + y²
b, ( x-4y)²= x² -8xy² + 16y2
c, \(\left(3x+\frac{1}{3}\right)^2=9x^2+2xy+\frac{1}{9}\)
d,\(4x^2-81=\left(2x-9\right)\left(2x+9\right)\)
e,\(\left(xy+5\right)^2=x^2y^2+10xy+25\)
f,\(\left(x-y+z\right)^2=x^2+y^2+z^2-2xy+2xz-2yz\)
g,\(1-9y^2=\left(1-3y\right)\left(1+3y\right)\)
h,\(\left(m-\frac{2}{3}n\right)^2=m^2-\frac{4}{3}mn+\frac{4}{9}n^2\)