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If a is a root of 4x²+2x-1=0, then the other root is 1)3a³-4a 2) 4a³-3a 3) 3a³+4a 4) 4a³+3a


If a is a root of 4x²+2x-1=0, then the other root is


1)3a³-4a                          2) 4a³-3a                            3) 3a³+4a


4) 4a³+3a


Grade:10

2 Answers

Menka Malguri
39 Points
10 years ago

Let the other root be b.

According to the quadratic equation theory,

sum of roots=-(B/A)

so,a+b=-2/4=-1/2

b=-1/2a

I suggest you to check your question and post it again.

Hope that works.

Ashwin Muralidharan IIT Madras
290 Points
10 years ago

Hi Sudhanshu,

 

Note that the roots of this equation are {root(5)-1}/4 ------- which is cos72

and -{root(5)+1}/4 -----------which is -cos36.

 

Now -cos36 = cos(36+180) = cos(216) = cos(3*72)

Now cos3x = 4cos^3 x - 3cosx....

So if one root is "a" (=cos72), then the other root is 4a^3-3a..... and that would be option (2).

 

Best Regards,

Ashwin (IIT Madras).

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