If a , b and c are constants, such that x → 1 lim ( x − 1 ) 2 a x 2 + b x + c − 3 = 5 , find the value of a + c .
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Oh wow, I'm amazed that even though the numerator and denominator have different degrees, the limit can be finite.
Definitely worth a reshare.
The question is easy but what amazed me was the answer 69. Damn these university teachers are perverts !!. LOL
how about this bro? a = 20 b = 20 c = -31
same method!!! +1 :D
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For you who wondered what is the answer
Step 1 : Finding the value of a + b + c
lim x 1 ( x − 1 ) 2 a x 2 + b x + c − 3 . lim x 1 ( x − 1 ) 2 = 5 . 0
a + b + c − 3 = 0
a + b + c = 9
Step 2 : Finding another equation
lim x 1 ( x − 1 ) 2 a x 2 + b x + c − 3 . lim x 1 ( x − 1 ) = 5 . 0
lim x 1 ( ( x − 1 ) a x 2 + b x + c − 9 . a x 2 + b x + c + 3 1 ) = 0
lim x 1 ( ( x − 1 ) a ( x 2 − 1 ) + b ( x − 1 ) . a + b + c + 3 1 ) = 0
6 1 lim x 1 ( a ( x + 1 ) + b ) = 0
6 2 a + b = 0
2 a = − b and it makes c = 9 + a
Step 3 : Finding the value of a
lim x 1 ( x − 1 ) 2 a x 2 + b x + c − 3 = 5
lim x 1 ( ( x − 1 ) 2 a x 2 + b x + c − 9 . a x 2 + b x + c + 3 1 ) = 5
lim x 1 ( x − 1 ) 2 a x 2 − 2 a x + a . a + b + c + 3 1 = 5
6 a = 5
a = 3 0
now we can substitute a = 3 0 to the equation c = 9 + a we get c = 3 9 so the value of a + c = 6 9