已知m²＋2mn=13,3mn+2n²=21,则2m²+13mn+6n²-44的值为多少?
问题描述：
已知m²＋2mn=13,3mn+2n²=21,则2m²+13mn+6n²-44的值为多少?
答
m^2 + 2mn = 13 等式二边同时乘以2 ,可得 2m^2 + 4mn = 26
3mn+2n^2 = 21 等式二边同时乘以3,可得 9mn+6n^2= 63
上面二式相加,可得,2m^2 + 13mn + 6n^2 = 89
所以所求的式子= 89-44= 45