y‘=−acosec(b−x)cot(b−x)(−1) y‘=ycot(b−x) y‘‘=y‘cot(b−x)+y cosec2(b−x) y‘‘=y12y+y(1+y2y2)
yy‘‘=2(y′)2+y2
Let f(x,y)=√x2+y2+√x2+y2−2x+1+√x2+y2−2y+1+√x2+y2−6x−8y+25∀x,yϵR, then