If 9x2 + 16y2 = 60 and 3x + 4y = 6, then the value of xy

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9x² + 16y² = 60
and 3x + 4y = 6
On squaring,
9x² + 16y² + 2 × 3x × 4y = 36
⇒ 60 + 24xy = 36
⇒ 24xy = 36 – 60 = –24

⇒ xy = −	24	= – 1
	24