If 2x+3y=14 and 2x−3y=2, find the value of xy.
2x+3y=14, 2x−3y=2we know that(a+b)2−(a−b)2=4ab∴ (2x+3y)2−(2x−3y)2=4×2x×3y=24xy⇒ (14)2−(2)2=24xy⇒ 24xy=196−4=192⇒ xy=19224=8∴ xy=8
If 2x+3y=8 and xy=2, find the value of 4x2+9y2.