Question

已知（a+b）的2次方=9,（a-b）的2次方=4,求a的2次方+b的2次方和ab的值

Answer 1

(a+b)^2=a^2+b^2+2ab=9--------------------------(1)

(a-b)^2=a^2+b^2-2ab=4---------------------------(2)

a^2+b^2={(1)+(2)}/2=13/2

ab={(1)-(2)}/4=5/4