已知m+n=9,mn=14,求3m²+3n²的值

已知m+n=9,mn=14,求3m²+3n²的值
已知m+n=9,mn=14,求3m²+3n²的值

已知m+n=9,mn=14,求3m²+3n²的值
3m²+3n²
=3(m²+n²)
=3[(m²+n²+2mn)-2mn]
=3(m+n)²-6mn
=3×9²-6×14
=3×81-84
=243-84
=159

3m²+3n²=3(m+n)^2-6mn=3*9*9-14*6=159
不懂可以再问，希望对你有帮助

3m²+3n²
=3(m²+n²)
=3(m²+n²+2mn)-6mn
=3(m+n)²-6mn
=3*9²-6*14
=3*81-84
=243-84
=159

3m²+3n²=3(m²+n²)=3((m+n)²-2mn)=3(81-28)=3×53=159;