/ Class 8 · Chapter 4: Cubes and Cube Roots Function Lab

The Cube Explosion

Why cubing a number makes it grow much faster than squaring.

Equation
y = x^1
Graph
-6-22610-40004008001.2k1.6kg2xy
Table
xy
-5-5
-4-4
-3-3
-2-2
-1-1
00
11
22
33
44
55
66
77
88
99
1010

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Selina ICSE: Cubes and Cube Roots

What this lesson covers

What you do

You shape the function y = x^k and watch the graph answer.

Challenges to clear

  • Turn the power dial k to 3: cubes! Check 3³ = 27 in the table.
  • The explosion: 5³ = 125, while squaring only reached 25.
  • Turn the power dial to cubes — slide k to 3.
  • There is a multiplier as well. Slide a until x = 2 reads 16: 2³ is 8, so a is 2.

Check yourself

Why does the graph of y = x^3 rise much steeper than y = x^2 for x > 2?

  • Because cubing multiplies the number by itself three times, adding an extra factor of x. — correct
  • Because the cube function has a higher starting point on the y-axis.
  • Because squares only work for positive numbers, but cubes work for all.
  • Because the graph of x^3 is a straight line, while x^2 is curved.

Think about it

  • At k = 2, x = 5 gives 25. How big will x = 5 be at k = 3?
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