- xy + 9= 9 xy=8
18
27
36
45
54
63
72 9 x 8= 72
81
90
2) x2-2ax+a(a+1)=0
D<0
D=x2-4ac<0
(-2ax)^2-4a(a+1)<0
4a-4a-4a<0
xE(0: ∞)
3) ?
4) 1pen+3books+5rulers= 670 350(pen)+ 5(rulers)x40=200 3(books)x40=120
1pen+5books+7rulers= 830
1pen+2rulers= ?
830-670= 160
2books+2rulers=160 and each 1 is 40
1book+1ruler=80
6(books and rulers)x40x2= 600
1pen= 350, so 1pen+2rulers= 430
5) x^2-4x+a>0
= D>0 = 16-4a>0
16= 0
a<4