Let f ( x ) be a piecewise function such that: f ( x ) = ⎩ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎧ ( x − 1 ) 2 x 2 3 2 − ( 4 1 6 ) x + 4 1 6 − 1 k , x = 1 , x = 1
Let k = a b × ( a c − 1 ) , where the value of k make f ( x ) continuous at 1.
If a is a prime number and b < c , solve for a + b + c .
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Applying the three conditions to make a function continuous at a value a,
1 s t condition: lim x → a f ( x ) exists.
f ( x ) = ( x − 1 ) 2 x 2 3 2 − ( 4 1 6 ) x + 4 1 6 − 1 , a = 1 ⟹ x → 1 lim ( x − 1 ) 2 x 2 3 2 − ( 4 1 6 ) x + 4 1 6 − 1 = lim x → 1 ( x − 1 ) 2 lim x → 1 ( x 2 3 2 − ( 4 1 6 ) x + 4 1 6 − 1 ) = lim x → 1 ( 2 ( x − 1 ) ) lim x → 1 ( ( 2 3 2 ) x 2 3 2 − 1 − 4 1 6 ) = lim x → 1 ( 2 ) lim x → 1 ( ( 2 3 2 ) ( 2 3 2 − 1 ) x 2 3 2 − 2 ) = x → 1 lim ( ( 2 3 1 ) ( 2 3 2 − 1 ) x 2 3 2 − 2 ) = ( 2 3 1 ) ( 2 3 2 − 1 )
Note: f ( x ) = ( x − 1 ) 2 x 2 3 2 − ( 4 1 6 ) x + 4 1 6 − 1 was used as we are dealing with limits.
2 n d condition: f ( a ) exist:
f ( x ) = k , a = 1 ⟹ f ( 1 ) = k
Note: f ( x ) = k was used as we are dealing with the function value.
3 r d condition: lim x → a f ( x ) = f ( a )
x → 1 lim f ( x ) = ( 2 3 1 ) ( 2 3 2 − 1 ) , f ( 1 ) = k ⟹ k = ( 2 3 1 ) ( 2 3 2 − 1 ) ⟹ a = 2 , b = 3 1 , c = 3 2 ∴ a + b + c = 2 + 3 1 + 3 2 = 6 5
The red and blue colored ones was obtain by applying L'Hôpital's Rule .