# The transformed equation of $x^2+6xy+8y^2=10$ when the axes are rotated through an angle $\large\frac{\pi}{4}$ is :

$\begin {array} {1 1} (a)\;15x^2-14xy+3y^2=20 & \quad (b)\;15x^2+14xy-3y^2=20 \\ (c)\;15^2+14xy+3y^2=20 & \quad (d)\;15x^2-14xy-3y^2=20 \end {array}$

## 1 Answer

$(c)\;15^2+14xy+3y^2=20$
answered Nov 7, 2013 by

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