Let y=f(x) be a thrice differentiable function in (-5,5). Let the tangents to the curve y=f(x) at (1,f(1)) and (3,f(3)) make angles /6 and /4, respectively with positive x-axis. If 27 13 ( (f'(t) )2+1 )f''(t) dt= + 3 where , are integers, then the value of + equals
- 26
- -16
- 36
- -14
Answer
(1) 26
Solution
Slope of tangent =f'(x): f'(1)= 6= 1 3, f'(3)= 4=1
Put f'(t)=z f''(t) dt=dz
13 ((f'(t))2+1 )f''(t) dt= 1/ 31(z2+1) dz= [ z33+z ]1/ 31
= 43- ( 19 3+ 1 3 )= 43- 10 327
27 ( 43- 10 327 )=36-10 3 =36, =-10
∴ + =26
Answer: (1)