Did You Know what Actually is Point of Inflection ? ( Part-2 )

Calculus Level 5

From the point P ( h , 2 5 h ) , h R , ( h 1 ) P(h,2-5h),\ h \in \mathbb{R},\ ( h \neq 1) two distinct tangents are drawn to the curve :

y = x 3 3 x 2 a x + b y={ x }^{ 3 } - { 3x }^{ 2 } - ax +b .

Find value of a + b . a + b.


Try : part-1


The answer is 3.

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1 solution

Aman Rajput
May 31, 2021

Let I I be the point of inflexion which is given by y = 0 y''=0 and solving this we get inflexion point as I ( 1 , b a 2 ) I(1,b-a-2) . Using one point form and slope through first derivative at this point, first tangent can be written as y = ( a 3 ) x + b + 1 y=(-a-3)x+b+1 . Using two point form between I I and P P we can also get different form of same slope. So equating the slope we get a h 3 = b a 2 2 + 5 h 1 h \large -ah-3=\frac{b-a-2-2+5h}{1-h} Comparing coefficients of h h we get a = 2 , b = 1 \boxed{a=2,b=1}

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