1. Phân tích các đa thức sau thành nhântử
a) 2x2 - 2xy - 5x + 5y
b) 8x2 + 4xy - 2ã - ay
c) x3 - 4x2 + 4x
d) 2xy - x2 - y2 + 16
e) x2 - y2 - 2yz - z2
g)3a2 - 6ab + 3b2 - 12c2
3. Tính nhanh:
a) 37,5.8,5 - 7,5.3,4 - 6,6.7,5 + 1,5.37,5
b) 352 + 402 - 252 = 80.35
3. Tìm x, biết:
a) x3 - 1/9 = 0
b) 2x - 2y - x2 + 2xy - y2 = 0
c) x(x -30 = x - 3 = 0
d) x2 ( x - 3) + 27 - 9x = 0
\(a,2x^2-2xt-5x+5y\)
\(=\left(2x^2-5x\right)-\left(2xy-5y\right)\)
\(=x\left(2x-5\right)-y\left(2x-5\right)\)
\(=\left(2x-5\right)\left(x-y\right)\)
\(b,8x^2+4xy-2ax-ay\)
\(=\left(8x^2-2ax\right)+\left(4xy-ay\right)\)
\(=2x\left(4x-a\right)+y\left(4x-a\right)\)
\(=\left(4x-a\right)\left(2x+y\right)\)
\(c,x^3-4x^2+4x\)
\(=x^3-2x^2-2x^2+4x\)
\(=\left(x^3-2x^2\right)-\left(2x^2-4x\right)\)
\(=x^2\left(x-2\right)-2x\left(x-2\right)\)
\(=\left(x-2\right)\left(x^2-2x\right)=x\left(x-2\right)\left(x-2\right)\)
\(=x\left(x-2\right)^2\)
\(d,2xy-x^2-y^2+16\)
\(=-\left(x^2-2xy+y^2-16\right)\)
\(=-\left[\left(x-y\right)^2-4^2\right]\)
\(=-\left(x-y-4\right)\left(x-y+4\right)\)
\(e,x^2-y^2-2yz-z^2\)
\(=x^2-\left(y^2+2yz+z^2\right)\)
\(=x^2-\left(y+z\right)^2=\left(x-y-z\right)\left(x+y+z\right)\)
bài 3
a) 37,5 . 8,5-7,5.3,4-6,6.7,5 +1,5.37,5
=(37,5.8,5+1,5.37,5)-(7,5 .3,4+6,6.7,5)
=37,5(8,5+1,5)-7,5(3,4+6,6
=37,5.10-7,5.10
=10(37,5-7,5)
=10.30
=300
b)352+402-252+80.35
=352+2.40.35+402-252
=(352+2,40.35+402)-252
=(35+40)2 -252
=(35+40-25)(35+40+25)
=50.100
5000
