Let a , b , c be the roots of the equation 2 x 3 − 3 x 2 + 5 x − 7 = 0 then find a 1 + b 1 + c 1 . Answer is of the form y x where x and y are positive integers. Enter x + y .
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a 1 + b 1 + c 1 = a b c b c + a c + a b = − D / A C / A = − ( − 7 ) / 2 5 / 2 n=5,m=7 n+m=12
http://www4a.wolframalpha.com/Calculate/MSP/MSP672020496i75b610hh8100003ig243cgcg82h6c7?MSPStoreType=image/gif&s=40&w=325.&h=95. is the only available real solution for the equation i.e. approximately 1.4455
can you tell me what is the mistake in this can we write the equation as x(2x^2 - 3x +5) = 7 * 1 and by comparing we get x=1 or x = -1/2 or x=2 therefore 1/a + 1/b +1/c =-1/2 therefore x +y =1
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Can you be a little bit more clear about what you mean by 'comparing'?
That's exactly how I did it.
For any equation, (quad, tri., biquad,..) for an eq. with roots a1,b1,c1,d1......, the eq with roots 1/a1, 1/a2, 1/a3.... can be obtained by just reversing the coefficients..
In this case coeff are 2, -3 ,+5, -7. .. reversing coeffs, we have the new eq: -7(x^3) +5(x^2) -3(x)=2=0 this equations sum= 1/a +1/b + 1/c = -(-5/7)=5/7= x+y= 5+7==12..
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Yes, since the roots are a , b , and c , this means that:
( x − a ) ( x − b ) ( x − c ) = x 3 − 2 3 x 2 + 2 5 x − 2 7
⇒ x 3 − ( a + b + c ) x 2 + ( a b + b c + c a ) x − a b c = x 3 − 2 3 x 2 + 2 5 x − 2 7
⇒ a b + b c + c a = 2 5 a b c = 2 7
Since a 1 + b 1 + c 1 = a b c a b + b c + c a = 2 7 3 5 = 7 5 = y x
Therefore, x + y = 5 + 7 = 1 2