This unit is dedicated to showing you a variety of cool math tricks that can help you tackle some basic math problems with speed and great accuracy. We start with a math trick that you can use to square a number easily and fast.
Take a close look at the figure below! It shows how you can use a cool math trick to square a two-digit number much faster than the traditional way of doing it.
The goal is to rewrite one of the numbers being multiplied so that it will have 1 or more zeros.
At this point, there may be one thing that you may not quite understand. Why did we add 4^{2} to 10 × 18 ? Keep reading as we show you the math behind it!
10 × 18 = (14 - 4)(14 + 4)
10 × 18 = 14 × 14 + 14 × 4 - 14 × 4 - 4^{2}
10 × 18 = 14 × 14 + 56 - 56 - 4^{2}
10 × 18 = 14 × 14 - 4^{2}
Now, all we have to do is to add 4^{2} to both sides of 10 × 18 = 14 × 14 - 4^{2}
10 × 18 + 4^{2} = 14 × 14 - 4^{2} + 4^{2}10 × 18 + 4^{2} = 14 × 14 (Here we go!)
In general,
Let X and c be a natural number. If X + c or X - c gives a number that has 1 or more zeros, then you can multiply X by X easily using the equation X^{2} = (X + c)(X - c) + c^{2}
Jul 30, 21 06:15 AM
Learn quickly how to find the number of combinations with this easy to follow lesson.