已知a+b=-3,ab=1/5,求
(1)a^2+b^2.
(2)1/a+1/b
(3)(a-b)^2
(4)(a+2)(b+2)
已知a+b=-3,ab=1/5,求
(1)a^2+b^2.
(2)1/a+1/b
(3)(a-b)^2
(4)(a+2)(b+2)
解:(a+b)^2=a^2+b^2+2ab=9
∵ab=1/5
∴a^2+b^2=9-2/5=43/5
1/a+1/b=(a+b)/ab=-15
(a-b)^2=a^2+b^2-2ab=43/5-2/5=41/5
(a+2)(b+2)=ab+2b+2a+4=2(a+b)+ab+4=6+1/5+4=51/5