if -5 is a root of the quadratic equation 2x^2+px-15 =0 and tue quadratic equation p(x^2+x)+k=0has equal roots find the vakue of k.
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Preparing for icse math which is day after tomorrow?
saccomander:
Substitiute 5 with x in the first equation and then find p.
substitiute
Then substitute p in the second equation. After that there is a formula, D = b^2 - 4ac = 0. Use this
Answered by
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As -5 is a root of the following equation
Putting x= -5
i.e. 2(-5)^2 + -5p -15=0
50 -15-5p=0
35=5p
7 =p
Now ,
Putting p=7 we get ,
7(x^2+x)+k=0
7x^2+7x+k=0
As above equation has equal roots
b^2-4ac =0
49-4(7)(k)=0
49-28k=0
49=28k
49/28 =k
7/4 =k
Putting x= -5
i.e. 2(-5)^2 + -5p -15=0
50 -15-5p=0
35=5p
7 =p
Now ,
Putting p=7 we get ,
7(x^2+x)+k=0
7x^2+7x+k=0
As above equation has equal roots
b^2-4ac =0
49-4(7)(k)=0
49-28k=0
49=28k
49/28 =k
7/4 =k
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