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secondary 3 | E Maths
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Shermaine
Shermaine

secondary 3 chevron_right E Maths chevron_right Singapore

pls help

Date Posted: 9 months ago
Views: 126
Shermaine
Shermaine
9 months ago
x= -2.45 btw
Eric Nicholas K
Eric Nicholas K
9 months ago
This question appears like it comes from a graph-plotting questions. If so, the full question might be useful for readers.

In this instance, you can perform simultaneous equations on the curve and the line to get an equation in x. We work out way towards the required format.

The value of x, in this case, might not be necessary.
J
J
9 months ago
With this limited amount of info, the most that can be done is:

Sub x = -2.45,

(-2.45)³ + A(-2.45) + B = 0
-14.706125 - 2.45A + B = 0
B = 2.45A + 14.706125

This is analogous to y = 2.45x + 14.706125

Unless you have another value of x, it's not quite possible to proceed further.

There is an infinite number of (A,B) pairs that satisfy this equation.


However, if the actual question is like what Eric said above, then you'll have to equate the curve (assuming its quadratic) to the equation of another function that intersects it.

For example,

Let's say you were asked to plot the quadratic curve with equation y = 3x² - 8 and a reciprocal curve with equation y = -25/x on the same piece of graph paper.

Plotting these two graphs will yield one intersection point x ≈ -2.46 (3s.f)

(The best estimation from the graph yields x = -2.45 as it probably lies somewhere in the middle of the small box in the grid of the graph paper i.e between x = -2.4 and x = -2.5, subjected on the scale you use)


Equating the two,

3x² - 8 = -25/x

Multiply both sides by x,

3x³ - 8x = -25

3x³ - 8x + 25 = 0

Divide throughout by 3,

x³ - 8/3 x + 25/3 = 0

A = -8/3 or 2⅔
B = 25/3 or 8⅓

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