a. x2 + 6x + 9
= (x + 3)2
Thay x = 97 vào, ta được:
= (97 + 3)2
= 1002
= 10000
b. x3 - 9x2 + 27x - 27
= (x - 3)3
Thay x = 13, ta được:
= (13 - 3)3
= 103
= 1000
c. 9x2 + 42x + 49
= (3x + 7)2
Thay x = 1 vào, ta được:
= (3.1 + 7)2
= 102
= 100
d. 25x2 - 2xy + \(\dfrac{1}{25}y^2\)
= \(\left(5x-\dfrac{1}{5}y\right)^2\)
Thay \(x=\dfrac{-1}{5};y=-5\) vào, ta được:
= \(\left(5.\dfrac{-1}{5}-\dfrac{1}{5}.\left(-5\right)\right)^2\)
= 02
= 0
a)= \(\left(x+3\right)^2=\left(97+3\right)^2=100^2=10000\)
b)\(=\left(x-3\right)^3=\left(13-3\right)^3=10^3=1000\)
c)=\(\left(3x+7\right)^2=\left(10\right)^2=100\)
\(d\))\(=\left(5x-\dfrac{1}{5}y\right)^2=\left(-1+1\right)^2=0\)
