Question

If a-b=3, and ab=10,find:a^3-b^3.

Answer 1

Answer:

117

Step-by-step explanation:

ab=10

a=10/b

then a-b=3 will become 10/b - b=3 by substituting above value of b

after calculating we get the value of b as

b= -5 and a= -2 , for b= 2 and a= 5

then putting these values in a^3 - b^3 we get 117 in any case

Answer 2

Answer:

a – b = 3

⇒ (a – b)3 = (3)3

⇒ a3 – b3 – 3ab (a –b) = 27

⇒ a3 – b3 – 3 × 10 (3) = 27

⇒ a3 – b3 – 90 = 27

⇒ a3 – b3 = 27 + 90

⇒ a3 – b3 = 117

Alternative Method :

(a –b)3 = a3 – b3 – 3ab (a –b)

⇒ (3)3 = a3 – b3 – 3 × 10 (3)

⇒ 27 = a3 – b3 – 90

⇒ 27 + 90 = a3 – b3

⇒ 117 = a3 – b3

⇒ a3 – b3 = 117

Step-by-step explanation:

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