(9+r)²=(9-r)²+(r-9)²求解这个方程

问题描述:

(9+r)²=(9-r)²+(r-9)²求解这个方程

由(9+r)²=(9-r)²+(r-9)²,
(9+r)²=2(9-r)²
(1)9+r=√2(9-r)
9+r=9√2-√2r
r+√2r=9√2-9
(1+√2)r=9(√2-1)
r=9(√2-1)/(√2+1)
r1=9(√2-1)²。
(2)9+r=-√2(9-r)
r2=√(√2+1)²

(9+r)²=(9-r)²+(r-9)²81+18r+r²=81-18r+r²+r²-18r+81整理得:r²-54r+81=0配方得:(r-27)²-27²+81=0(r-27)²=648r-27=±√648r=27±18√2