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secondary 3 | A Maths
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Pooh pooh bear
Pooh Pooh Bear

secondary 3 chevron_right A Maths chevron_right Singapore

Pls help to check , thk

Date Posted: 3 years ago
Views: 152
J
J
3 years ago
Not correct.

We never assume the statement we want to prove. That is known as circular logic.
J
J
3 years ago
What it should be is :

x + ½ = 2x² + 5x

2x² + 5x - x - ½ = 0

2x² + 4x - ½ = 0

Divide both sides by 2,

x² + 2x - ¼ = 0

Next, check the discriminant ('b² - 4ac')

Discriminant = 2² - 4(1)(-¼)

= 4 + 1

= 5

Since 5 > 0, discriminant > 0.

This means that the equation has 2 real and distinct roots and therefore the curve y = 2x² + 5x intersects the line y = x + ½ at two distinct points.
Pooh pooh bear
Pooh Pooh Bear
3 years ago
Thk a lot
J
J
3 years ago
By the way, you have gotten your b and c mixed up.

Always write the equation in the form ax² + bx + c = 0

So depending on which side you bring the terms over to , you could have :

2x² + 4x - ½ = 0 →simplified to x² + 2x - ¼ = 0 ①

Or

-2x² - 4x + ½ = 0 → simplified to -x² - 2x + ¼ = 0 ②

You will get from one equation to the other when you multiply by - 1.

In the case of ②,

Discriminant = (-2)² - 4(-1)(¼)

= 4 + 1
= 5

Regardless of starting from ① or ②, the result is the same.
Pooh pooh bear
Pooh Pooh Bear
3 years ago
Thank for the advice
J
J
3 years ago
No problem. Do revise the quadratic formula and how to interpret it when you have time.

The whole idea of 2 distinct real roots, 1 equal real root and no real roots is based on the square root in that formula.

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Pooh pooh bear
Pooh Pooh Bear
3 years ago
Thik