Question

If a + b = 10 and ab = 10 then a^2 + b^2 = A) 80
B) 50
C) 20
D) 100

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Answer 1

Answer:

Given, (a+b)=7, ab=10

Squaring both sides

⇒(a+b)

2

=7

2

⇒a

2

+b

2

+2ab=49

⇒a

2

+b

2

=49−2(10)

⇒a

2

+b

2

=29

Now,

(a−b)

2

=a

2

+b

2

−2ab

=29−2(10)

=29−20

=9

∴a−b=

9

=±3