（m+15）x2-（3m+5）x+12=0的两根x1,x2是一个直角三角形两个锐角的正弦值
x1^2+x2^2=1
x1+x2=(3m+5)/(m+15),x1x2=12/(m+15)
x1^2+x2^2=(x1+x2)^2-2x1x2
=((3m+5)/(m+15))^2-2*12/(m+15)
=[(3m+5)^2-2*12(m+15)]/(m+15)^2
= (9m^2+6m-335)/(m+15)^2
所以(9m^2+6m-335)/(m+15)^2=1
(9m^2+6m-335)=(m+15)^2
(9m^2+6m-335)=m^2+30m+225
8m^2-24m-560=0
m^2-3m-70=0
(m-10)(m+7)=0
m1=10,m2=-7
因为m=-7时,x1+x2=(3m+5)/(m+15)=-16/8