m²-n²=(m+n)(m-n)
6=3(m+n)
m+n=2
(y³)²÷y^5
=y^(3×2-5)
=y
x²-5x=14
(x-1)(2x-1)-(x+1)²+1
=2x²-3x+1-x²-2x-1+1
=x²-5x+1
=14+1
=15