giúp tí hihi
13: \(x\left(a+b\right)+\left(a+b\right)\)
=(a+b)(x+1)
14: \(m\left(x-y\right)+x-y=m\left(x-y\right)+\left(x-y\right)=\left(x-y\right)\left(m+1\right)\)
15: \(x-y-a\left(x-y\right)=\left(x-y\right)-a\left(x-y\right)=\left(x-y\right)\left(1-a\right)\)
16: a-b-x(b-a)
=a-b+x(a-b)
=(a-b)(x+1)
20: a(x-y)-x+y
=a(x-y)-(x-y)
=(x-y)(a-1)
21: \(5a\left(a-2\right)-a+2=5a\left(a-2\right)-\left(a-2\right)=\left(a-2\right)\left(5a-1\right)\)
22: \(ax+ay+bx+by\)
=a(x+y)+b(x+y)
=(x+y)(a+b)
23: \(ax+ay-2x-2y\)
=a(x+y)-2(x+y)
=(x+y)(a-2)
24: \(x^2+xy-2x-2y\)
=x(x+y)-2(x+y)
=(x+y)(x-2)
25: \(a^2-4=a^2-2^2=\left(a-2\right)\left(a+2\right)\)
26: \(a^2-9=a^2-3^2=\left(a-3\right)\left(a+3\right)\)
27: \(\dfrac{1}{4}a^2-\dfrac{1}{9}b^2=\left(\dfrac{1}{2}a\right)^2-\left(\dfrac{1}{3}b\right)^2\)
\(=\left(\dfrac{1}{2}a-\dfrac{1}{3}b\right)\left(\dfrac{1}{2}a+\dfrac{1}{3}b\right)\)
28: \(\left(a-b\right)^2-c^2=\left(a-b-c\right)\left(a-b+c\right)\)
29: \(x^2+2x+1=x^2+2\cdot x\cdot1+1^2=\left(x+1\right)^2\)
30: \(x^2+8x+16=x^2+2\cdot x\cdot4+4^2=\left(x+4\right)^2\)
31: \(x^2-x-6\)
\(=x^2-3x+2x-6\)
=x(x-3)+2(x-3)
=(x-3)(x+2)
32: \(x^2-2x-3=x^2-3x+x-3\)
=x(x-3)+(x-3)
=(x-3)(x+1)
33: \(x^2-5x+6=x^2-2x-3x+6\)
=x(x-2)-3(x-2)
=(x-2)(x-3)
34: \(x^2-7x+12=x^2-3x-4x+12\)
=x(x-3)-4(x-3)
=(x-3)(x-4)
35: \(x^2+x-12=x^2+4x-3x-12\)
=x(x+4)-3(x+4)
=(x+4)(x-3)
36: \(x^2-9x+20\)
\(=x^2-4x-5x+20\)
=x(x-4)-5(x-4)
=(x-4)(x-5)
37: \(x^2+x-20=x^2+5x-4x-20\)
=x(x+5)-4(x+5)
=(x+5)(x-4)
38: \(4x^2-4x-3\)
\(=4x^2-6x+2x-3\)
=2x(2x-3)+(2x-3)
=(2x-3)(2x+1)
39: \(4x^2+5x-6\)
\(=4x^2+8x-3x-6\)
=4x(x+2)-3(x+2)
=(x+2)(4x-3)
40: \(2x^2-3x-2\)
\(=2x^2-4x+x-2\)
=2x(x-2)+(x-2)
=(x-2)(2x+1)
