Question

已知a+b=10,ab=20,求a的平方+b的平方；（a-b）的平方

Answer 1

解：
a的平方+b的平方
=(a+b)²-2ab
=10²-2×20
=60
（a-b）的平方
=（a+b）²-4ab
=10²-4×20
=20

Answer 2

a的平方+b的平方
=a²+2ab+b²-2ab
=(a+b)²-2ab
=100-40
=60
（a-b）的平方
=a²-2ab+b²
=a²+2ab+b²-4ab
=(a+b)²-4ab
=100-80
=20

Answer 3

a的平方+b的平方
=a²+2ab+b²-2ab
=(a+b)²-2ab
=10²-2*20
=100-40
=60

(a-b)²
=a²-2ab+b²
=60-2*20
=20

Answer 4

1 a²+b²
=（a+b）²-2ab
=10²-2×20
=100-40
=60
2（a-b）²
=a²+b²-2ab
=60-2×20
=20

Answer 5

a²+b²
=（a+b）²-2ab
=100-40
=60
（a-b）²
=a²+b²-2ab
=60-40
=20

Answer 6

(a+b)^2=100
a^2+b^2+2ab=100 其中ab=20
a^2+b^2=60
(a-b)^2
=a^2+b^2-2ab
=60-2*20
=20