(3m+3n+1(3m+3n-1)=80,求M+N的值

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(3m+3n+1(3m+3n-1)=80,求M+N的值
(3m+3n+1(3m+3n-1)=80,求M+N的值

(3m+3n+1(3m+3n-1)=80,求M+N的值
(3m+3n+1(3m+3n-1)=80
(3m+3n)^2-1^2 = 80
(3m+3n)^2 = 80 + 1 = 81
---> [3(m+n)]^2 = 81
(m+n)^2 = 9
m+n = 3 或者m + n = -3

原式=9(m+n)²-1=80
(m+n)²=9
(m+n) =3或者(m+n) =-3

27

(3m+3n)^2-1=80
3m+3n=9或-9
m+n=3或-3

(3m+3n+1)(3m+3n-1)=80 是这个题吧- -
M+N=正负3

设(m+n)=k
则:(3k+1)(3k-1)=80
9k^2-1=80
k^2=9
k=+3或-3