3 years ago

If x^2+25y^2=416 and x-5y=-16 the value of xy is a)16 b)8 c)-8 d)-16

Mathematics

1 answer:

pshichka [43]3 years ago

3 0

Answer:

(a)

Step-by-step explanation:

Note the expansion of (x - 5y)² is

(x - 5y)² = x² - 10xy + 25y² , that is

(x - 5y)² = x² + 25y² - 10xy ← substitute given values

(- 16)² = 416 - 10xy

256 = 416 - 10xy ( subtract 416 from both sides )

- 160 = - 10xy ( divide both sides by - 10 )

xy = 16 → (a)

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