Quadratics help

I'm trying to solve 5x^2 + 4x - 3 = 0. I get stuck when im multiplying out the discriminant. As it is b^2 - 4ac , do I multiply a & c by -4 because of the negative sign in front of the 4? Or do I multiply a&c by 4 and then subtract it from b^2.

Thanks in advance

Reply 1

username1560589

20

Original post by doglover123

I'm trying to solve 5x^2 + 4x - 3 = 0. I get stuck when im multiplying out the discriminant. As it is b^2 - 4ac , do I multiply a & c by -4 because of the negative sign in front of the 4? Or do I multiply a&c by 4 and then subtract it from b^2.

Thanks in advance

Depends what mood you're in.

Reply 2

Makadia

2

Original post by doglover123

I'm trying to solve 5x^2 + 4x - 3 = 0. I get stuck when im multiplying out the discriminant. As it is b^2 - 4ac , do I multiply a & c by -4 because of the negative sign in front of the 4? Or do I multiply a&c by 4 and then subtract it from b^2.

Thanks in advance

b^2 - (4ac)

Posted from TSR Mobile

Reply 3

shaz39

1

You don't need to calculate the discriminant to solve that equation.

For this particular problem, use the quadratic equation.

Anyhow, the answer to your question is what you said first, not the second part. You do a*c then multiply that by (-4).

Reply 4

awais_k

2

Original post by doglover123

I'm trying to solve 5x^2 + 4x - 3 = 0. I get stuck when im multiplying out the discriminant. As it is b^2 - 4ac , do I multiply a & c by -4 because of the negative sign in front of the 4? Or do I multiply a&c by 4 and then subtract it from b^2.

Thanks in advance

This is GCSE , isn't it

Reply 5

StevieC33

2

Just multiplying by -4 is easier for me, as it sorts out what's negative, and what's positive straight away.

Reply 6

Makadia

2

Original post by awais_k

This is GCSE , isn't it

Yeah and Core 1

Posted from TSR Mobile

Reply 7

awais_k

2

Original post by Makadia

Yeah and Core 1

Posted from TSR Mobile

Ah ok.

OP, just label it a,b,c then put it into the quadratic equation, simple.

Reply 8

Muttley79

20

The discriminant is part of the quadratic formula ...

Reply 9

StevieC33

2

Original post by awais_k

Ah ok.

OP, just label it a,b,c then put it into the quadratic equation, simple.

Though, he may be doing the step to find out what type of answer he'll get,
b^2-4ac=0
b^2-4ac>0
b^2-4ac<0

Reply 10

Makadia

2

Original post by shaz39

You don't need to calculate the discriminant to solve that equation.

For this particular problem, use the quadratic equation.

Anyhow, the answer to your question is what you said first, not the second part. You do a*c then multiply that by (-4).

Would it not be the the second part because if you use (-4)ac, you have to add that to the b^2, so the discriminant would be b^2+(-4ac). Whereas if you didn't have the '+' in the middle, and you use (-4), you would have b^2 (-4ac).

Posted from TSR Mobile