a^2-4a+9b^2+6b+5=0
(a²-4a+4)+(9b²+6b+1)=0
(a-2)²+(3b+1)²=0
a-2=0,3b+1=0
a=2,b=-1/3
a^2-6ab+9b^2
=(a-3b)²
=[2-3×(-1/3)]²
=3²
=9
a^2-4a+9b^2+6b+5=0
(a²-4a+4)+(9b²+6b+1)=0
(a-2)²+(3b+1)²=0
a-2=0,3b+1=0
a=2,b=-1/3
a^2-6ab+9b^2
=(a-3b)²
=[2-3×(-1/3)]²
=3²
=9