Lets example to understand this method(x + 3) (3x + 4)
Step IWrite one binomial under the other binomial as shown underx + 33x + 4 Multiply the digits on right side column vertically3× 4 = 12
Step 2x + 33x + 4
Now multiply cross wise and add. Shown as under(x × 4) + (3x × 3)
4x + 9x = 13x
Step 3x + 33x + 4
Now vertically multiply on left hand side columnx × 3x = 3x2
So, The answer is = 3x2 + 13x + 12
Lets another example to understand it
(2x2 + x + 5) (3x2 + 2x + 6)
Step 1Write one trinomial under the other as shown below
2x2 + x + 5
3x2 + 2x + 6
On left hand side column , multiply vertically
2x2 × 3x2 = 6x4
Step 2Now Cross wise multiplication with first two columns
2x2 + x + 5
3x2 + 2x + 6
= (2x2 × 2x) + (3x2 × x)
= 4x3 + 3x3
= 7x3
Step 3Now multiply cross wise extreme left and extreme right columns
Multiply Middle Column vertically
And add the all three products. As shown below
2x2 + x + 5
3x2 + 2x + 6
= (2x2 × 6) + (3x2 × 5) + ( x × 2x)
= 12x2 + 15x2 + 2x2
= 29x2
Step 4Now multiply cross wise middle column with extreme last column (right side)
2x2 + x + 5
3x2 + 2x + 6
= (2x × 5) + (x × 6)
10x + 6x
= 16x
Step 5Right Hand side Vertically Multiplication
2x2 + x + 5
3x2 + 2x + 6
= 5 × 6
= 30
Answer = 6x4 + 7x3 + 29x2 + 16x + 30
Practise it: vertically and crosswise works the same way on plain numbers, so try it in our multiplication game.