Answer: m²-9mn+2n²
Step-by-step explanation: make use of BODMAS strategy. Let the unknown be x.
-7mn+2m²+3n²-x= m²+2mn+n². Since we are concerned about getting the unknown,let's try to collect the like terms.
-7mn+2m²+3n²-(m²+2mn+n²)= x
-7mn+2m²+3n²-m²-2mn-n²= x
-7mn-2mn+2m²-m²+3n²-n²=x
-9mn+m²+2mn= x
X= m²-9mn+2n²
