Question

If a + b = 9 and ab = 20, find the value of (a 2 + b 2 ).
(show working)

Answer 1

Answer:

a²+b² = (a+b)²-2ab

=(9)²-2×20

=49 - 40

=9 Ans

Answer 2

Step-by-step explanation:

| If a + b = 9 and ab = 20, then a2 + b2 will be

⏺ A.

41

⏺ B.

40

⏺ C.

39

⏺ D.

36

Right answer is a: A

SOLUTION

By putting the values a + b = 9 and ab = 20, in the identity (a + b)2 = a2 + b2 + 2ab We have 92 = a2 + b2 + 2 20 81 = a2 + b2 + 40 a2 + b2 = 81 – 40 = 41