8
(b+4)²+(2b-5)(2b+5)=b²+8b+16+4b²-25=5b²+8b-9
10
(9/a²-16/b²)*1/(8a-6b)=(9b²-16a²)/a²b²*1/(8a-6b)=(3b-4a)(3b+4a)/a²b²*1/2(4a-3b)=
=-(3b+4a)/2a²b²
20
(5x²-9x-2)/(10x²+22x+4)=(5x+1)(x-2)/
5x²-9x-2=5(x+1/5)(x-2)=(5x+1)(x-2)/(2x+4)(5x+1)=(x-2)/(2x+4)
D=81+40=121
x1=(9-11)/10=-1/5
x2=(9+11)/10=2
10x²+22x+4=10(x+2)(x+1/5)=(2x+4)(5x+1)
D=484-160=324
x1=(-22-18)/20=-2
x2=(-22+18)/20=-1/5