If X²+(3k+1)x+(4-9k) show that 9k²+42k-15

KingRich

See attached:

Please don’t tell me this is another error?

I found b=30k.

(edited 12 months ago)

Reply 1

prathams07

heya! repeated roots means b²-4ac is 0. your b value is (3k-1) a value is 1 and c value is (4-9k). sub these values into b²-4ac, expand and simplify, that should give you the ans

Reply 2

prathams07

Original post by KingRich

See attached:

Please don’t tell me this is another error?
I found b=30k.

also k is not equal to b²-4ac

Reply 3

tonyiptony

Well, there is in fact an error in the question, in that x^2+(3k+1)x+(4-9k) is not a quadratic equation. That said I suspect you probably aren't looking at this being the error.

The correct approach is as above.

Reply 4

username6691833

Original post by KingRich

See attached:

Please don’t tell me this is another error?
I found b=30k.

The major error is that b^2 - 4ac =0 not k. also, you noted the expression for b wrong...

Reply 5

KingRich

Original post by prathams07

heya! repeated roots means b²-4ac is 0. your b value is (3k-1) a value is 1 and c value is (4-9k). sub these values into b²-4ac, expand and simplify, that should give you the ans

I know what a repeated root means. I think you should re-read my original op. I already gave the solution. I wasn’t asking how to find it.

k is used to represent the integer. In this instance, I have to show k=0. So, because k represents the discrimination and so does the formula. Equating them means exactly the same.

Reply 6

KingRich

Original post by WordsFiddle

The major error is that b^2 - 4ac =0 not k. also, you noted the expression for b wrong...

I noted b wrong? Oh, crap thank you

Reply 7

KingRich

Original post by WordsFiddle

The major error is that b^2 - 4ac =0 not k. also, you noted the expression for b wrong...

also, two of you seem confused as to why I equate k=b^2-4ac.... How To Determine The Discriminant of a Quadratic Equation - YouTube... this video will explain it.

Reply 8

tonyiptony

Original post by KingRich

also, two of you seem confused as to why I equate k=b^2-4ac.... How To Determine The Discriminant of a Quadratic Equation - YouTube... this video will explain it.

I'm not sure I follow why you think the discriminant = k when there the quadratic has repeated roots.

Remember the discriminant is exactly whatever goes inside the square root in the quadratic formula, and it precedes by a plus or minus sign, hence giving potentially 1 or 2 unique solutions. So if the discriminant is k, the roots are then "blah + sqrt(k)" and "blah - sqrt(k)", which might not be repeated...

(edited 12 months ago)

Reply 9

username6691833

Original post by KingRich

also, two of you seem confused as to why I equate k=b^2-4ac.... How To Determine The Discriminant of a Quadratic Equation - YouTube... this video will explain it.

Oh so "k" given in the equation is not the same as what you equated b^2-4ac?

(The video just repeats what we already know about discriminants but thnx)

Reply 10

KingRich

Original post by WordsFiddle

Oh so "k" given in the equation is not the same as what you equated b^2-4ac?
(The video just repeats what we already know about discriminants but thnx)

My error, I was meant to say D=b²-4ac.

Reply 11

KingRich

Original post by tonyiptony

I'm not sure I follow why you think the discriminant = k when there the quadratic has repeated roots.
Remember the discriminant is exactly whatever goes inside the square root in the quadratic formula, and it precedes by a plus or minus sign, hence giving potentially 1 or 2 unique solutions. So if the discriminant is k, the roots are then "blah + sqrt(k)" and "blah - sqrt(k)", which might not be repeated...

I understand where the discriminant is and where it comes from within the quadratic formula. I also know if k=0 it’s a repeated root and k<0 has no roots and k>0 has two real roots..

I made the error of saying k but i was meant to say D=b²-4ac. It’s been a long day lol