2. а) а²-12а+36=а²-2*а*6+6²=(а-6)² б) 25-х²=5²-х²=(5-х)(5+х)
3.а) 36-(6-х)²=х(4-х) б)81-х²=0
36-(6²-2*6*х+х²)=4х-х² 81=х²
36-36+12х-х²-4х+х²=0 х=9 х=-9
8х=0
х=0
пров. 36-(6-0)²=36-36=0
0*(4-0)=0
4.а) (а+5)²-(15+10а)=а²-2*а*5+5²-15-10а=а²-10а+25-15-10а=а²-20а+10
б)(4+у)²(4-у)²=(4+у)(4+у)(4-у)(4-у)=((4+у)(4-у))*((4+у)(4-у))=
=(4²-у²)(4²-у²)=(16-у²)(16-у²)=(16-у²)²