Question

Find the value of 8x^3-y^3 if 2x-y=3 and xy= -1

Answer 1

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Answer 2

Answer:

9

Step-by-step explanation:

8x^3-y^3 = ?

2x-y=3

xy= -1

8x³ - y³

= (2x)³ -y³

as we know that a³ - b³ = (a-b)(a² + b² + ab)

Here a = 2x & b = y

= (2x -y)((2x)² + y² + 2xy)

we know a² + b² = (a-b)² + 2ab

a = 2x  & b = y

=(2x -y)((2x-y)²+ 2(2x)y + 2xy)

=(2x-y)( (2x-y)² + 6xy)

now putting value of 2x- y = 3  & xy = -1

= (3)×( 3² + 6×(-1))

= 3 × (9 - 6)

= 3 × 3

= 9