



 
Hi Monica, When you differentiate y in this expression you should get y' not y*y'. Hence the first line should be \[\cos(xy) \times [x \times y' + y \times x'] = 2x  y'\] which becomes \[\cos(xy) \times [x \times y' + y \times 1] = 2x  y'\] Can you see how to complete it now? Write back if you need more help. Penny  


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