Question

If 3x - 7y=8 and xy=-1,find the value of 9x square + 49y square

Answer 1

Answer:

Step-by-step explanation:

(3x-7y)^2=8^2

9x^2+49y^2-42xy=64

9x^2+49y^2-42(-1)=64

9x^2+49y^2+42=64

9x^2+49y^2=64-42

9x^2+49y^2=22

This is your answer

Hope it helps you

Answer 2

Answer:

22

Step-by-step explanation:

Given 3x-7y=8 and xy=1

Square both sides of equation 3x-7y=8

      i.e (3x-7y)² = 8²

        ⇒ 9x² + 49y² + 2(3x)(-7y) = 64            [ (a+b)² = a²+b²+2ab ]

        ⇒ 9x² + 49y² - 42x  = 64  

   replace xy with 1

         ⇒ 9x² + 49y² - 42(1) = 64

         ⇒ 9x² + 49y² = 64 - 42= 22

Therefore 9x² + 49y²  =22

Hope this helps