Question

1.已知实数a,b满足（a+b）的2次方=1,（a-b)的2次方=25,求a的2次方+b的2次方+ab的值得多少

Answer 1

1 (a+b)^2=1.(1)

(a-b)^2=25.(2)

(1)+(2):2a^2+2b^2=26

a^2+b^2=13

(1)-(2):4ab=-24,ab=-6

a^2+b^2+ab

=13-6

=7

2.(x-y+1)(x+y-5)

=x^2 +xy-5x-xy-y^2+5y+x+y-5

=x^2-4x-y^2 +6y -5