8. If 2x + 3y = 8 and xy = 2, find the value of 4x2 + 9y?
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Answer:
40
Step-by-step explanation:
(2x + 3y) = 8 ----(i)
xy = 2
Squaring equation (i) ;
(2x + 3y)² = 8²
=> 4x² + 9y² + 2.(2x).(3y) = 64
=> 4x² + 9y² + 12xy = 64
=> 4x² + 9y² = 64 - 12xy
=> 4x² + 9y² = 64 - 12 x 2
=> 4x² + 9y² = 64 -24
=> 4x² + 9y² = 40
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