KCET2010MathematicsApplication of Derivatives
For the curve 4 x⁵=5 y⁴ , the ratio of the cube of the subtangent at a point on the curve the square of the subnormal at the same point is
Options
- A4⁴ 5
- B5⁴ 4
- C4⁴ 5⁴
- D( 5 4 )⁴
Correct answer
C. 4⁴ 5⁴
Step-by-step solution
The given curve is 4 x⁵=5 y⁴ gathered 20 x⁴=20 y³ d y d x d y d x = x⁴ y³ gathered We know that Length of subnormal (S N)= (y d x d y )= ( y⁴ x⁴ ) Length of subtangent ( ST )= ( y dy dx )= ( x ⁴ y ² ) But given condition is aligned ( SN )³ ( ST )² = ( y ⁴ / x ⁴ )³ ( x ⁴ / y ² )² = ( y ⁴ x ⁴ )³ ( y ² x ⁴ )² = y ¹² x ¹² y ⁴ x ⁸ = ( y ¹⁶ x ²⁰ ) = ( y ⁴ x ⁵ )⁴ = ( 4 5 )⁴= 4⁴ 5⁴ ( 4 x ⁵=5 y ⁴ ) aligned