a) x² - y² = (x+y)(x-y)

Thay x=87; y=13 có:

(87+13)(87-13) = 100.74 = 7400

b)x³-3x²+3x-1 = x³ - 3x².1+ 3x .1² -1³ = (x-1)³

Thay x=101 có:

(101-1)³ =100³ =1000000

c)x³+9x²+27x+27= x³ +3x².1+3x.1²+3³= (x+3)³

^{Thay x=97 có:}

(97+3)³= 100³=1000000