Question

If 3x +2y =12 and xy=6 find value of 9xsquare +4y square

Answer 1

square on both sides

( 3x + 2y ) square =12 square

(3x + 2y ) square = 144

now use ( a+b ) square formula

= a square + 2ab + b square

=( 3x ) square + 2 X 3x X 2y + ( 2y ) square = 144

= 9x square + 12xy + 4y square = 144

we know xy = 6

= 9x square + 12 X 6 + 4y square = 144

= 9x square + 72 + 4y square = 144

now remove the constant

= 9x square + 4y square = 144 - 72

= 9x square + 4y square = 72