Nehal Wani
Last Activity: 14 Years ago
If 5f(x)+3f(1/x)=x+2 and y=xf(x), then dy/dx at x=1
5f(x)+3f(1/x)=x+2
25f(x)+15(1/x)=5x+10…………………..(i)
Replacing x with 1/x,
5f(1/x)+3(x)=1/x+2
15f(1/x)+9f(x)=3/x+6………………………(ii)
(i)-(ii)
16f(x)=5x-3/x+4
f(x)=5x/16-3/16x+1/4
y=xf(x)=5x2/16-3/16+x/4
dy/dx=10x/16+1/4
dy/dx at x=1 is 10/16+1/4=7/8