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← JEE Main 2015 · 4 Apr · Shift 1
MathematicsSingle correct+4 / -1Question 71 of 90

JEE Main 2015 · 4 Apr · Shift 1, Mathematics question 71

If the function.
g(x)={kx+1,0≤x≤3mx+2,3<x≤5g(x)=\begin{cases}k\sqrt{x+1},&0\le x\le3\\mx+2,&3<x\le5\end{cases}
is differentiable, then the value of k+mk+m is :

Choose one option
Answer and worked solution

Official answer: A

  • Continuity at 3: 2k=3m+22k=3m+2.
  • Equal derivatives: k24=m\dfrac k{2\sqrt4}=m, i.e. m=k4m=\frac k4.

Then 2k=3k4+22k=\frac{3k}4+2, so k=85k=\frac85, m=25m=\frac25 and k+m=2k+m=2.