notentirely 1) а) (x+2)2+(2x-1)2= x2+4x+4+4x2-4x+1=5x2+5=5(x2+1)
б)(10-7y)(7y+10)=100-49y2
в) (2+а)(4-2а+а2)=8+а3
г) (а+3)3=а3+9а2+27а+27

2) 100а2-20а+1=(10-1)2
81x2-25y2=(9x-5y)(9x+5y)
27x3-125y3=(3x-5y)(9x2+15xy+25y2)
x4-x3-x+1=(x-1)