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secondary 3 | A Maths
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LockB
LockB

secondary 3 chevron_right A Maths chevron_right Singapore

need help with 7 and 8c,pls explain too

Date Posted: 3 years ago
Views: 191
LockB
LockB
3 years ago
no need help with 8c anymore
J
J
3 years ago
Use Desmos.com and sketch the graphs.
b) basically is the number of points wherr they intersect.
LockB
LockB
3 years ago
what is y=2/pi x tho, like how to draw it during exam
J
J
3 years ago
y = 2/π x is a straight line, just like your usual y = 5x, y = 12x , y = 2x + 5 etc.

y = mx + c is your usual equation of a straight line.

In this case your m = 2/π and c = 0.

2/π is just 2 ÷ π
2 ÷ π ≈ 0.63661977....
J
J
3 years ago
Since you're asked to draw for the domain of 0 ≤ x ≤ 2π,

You know that when x = 0, y = 2/π × 0 = 0

When x = 2π, y = 2/π × 2π = 4

So for this straight line, just mark the coordinates (0,0) and (2π, 4) and join them.
LockB
LockB
3 years ago
usually just find the coordinates by inserting x=0 or x=2pi (or 3pi if the range ends at 3pi) into the equation then connect the 2points together?
J
J
3 years ago
It works for the equation of any straight line with a given domain.

If you had for example, y = 3x + 6 for the domain -3 ≤ x ≤ 10,

Sub x = -3 and x = 10 since they are the boundaries of your domain.

You'll get y = -3 and y = 36 respectively.

Plot (-3,-3) and (10,36) and join them.

Anywhere on this line, the gradient is the same.
Eric Nicholas K
Eric Nicholas K
3 years ago
Some of my students panick when they see such equations y = (2/pi) x. I think it’s because they are quite used to whole numbers or rational fractions as the gradient.

LockB, we draw such lines as usual. If we are provided with the range say 0 to 2pi, we can just substitute these limits to find the coordinates which would be (0, 0) and (2pi, 4).

The purpose of putting a pi in the denominator of the equation of the line is so that you have a nice y-value for sketching on your graph.
J
J
3 years ago
The 2/π makes the coordinates easy to plot.

As for 2/π itself, they should always be aware that π = 3.141592653...

It is a real number, and not a variable, so there's nothing to worry.

The setters could easily switch the question to another real transcendental number like e .

(though at this level we wouldn't expect things like the golden ratio (φ) = (1+√5) / 2 or Apéry's constant (ζ(3) ≈ 1.2020569031595942854...)

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