FOIL Method - Table As An Alternative To FOIL

Table As An Alternative To FOIL

A visual memory tool can replace the FOIL mnemonic for a pair of polynomials with any number of terms. Make a table with the terms of the first polynomial on the left edge and the terms of the second on the top edge, then fill in the table with products. The table equivalent to the FOIL rule looks like this.

\begin{matrix}
\times & c & d \\
a & ac & ad \\
b & bc & bd
\end{matrix}

In the case that these are polynomials, the terms of a given degree are found by adding along the antidiagonals

\begin{matrix}
\times & cx & d \\
ax & acx^2 & adx \\
b & bcx & bd
\end{matrix}

so

To multiply (a+b+c)(w+x+y+z), the table would be as follows.

\begin{matrix}
\times & w & x & y & z \\
a & aw & ax & ay & az \\
b & bw & bx & by & bz \\
c & cw & cx & cy & cz
\end{matrix}

The sum of the table entries is the product of the polynomials. Thus

\begin{align} (a+b+c)(w+x+y+z) = {} & aw + ax + ay + az \\ & {} + bw + bx + by + bz \\ & {} + cw + cx + cy + cz .
\end{align}

Similarly, to multiply one writes the same table

\begin{matrix}
\times & d & e & f & g \\
a & ad & ae & af & ag \\
b & bd & be & bf & bg \\
c & cd & ce & cf & cg
\end{matrix}

and sums along antidiagonals:

\begin{align}(ax^2&+bx+c)(dx^3+ex^2+fx+g)\\
&= adx^5 + (ae+bd)x^4 + (af+be+cd)x^3 + (ag+bf+ce)x^2+(bg+cf)x+cg.\end{align}

Read more about this topic:  FOIL Method

Famous quotes containing the words table, alternative and/or foil:

    How to attain sufficient clarity of thought to meet the terrifying issues now facing us, before it is too late, is ... important. Of one thing I feel reasonably sure: we can’t stop to discuss whether the table has or hasn’t legs when the house is burning down over our heads. Nor do the classics per se seem to furnish the kind of education which fits people to cope with a fast-changing civilization.
    Mary Barnett Gilson (1877–?)

    A mental disease has swept the planet: banalization.... Presented with the alternative of love or a garbage disposal unit, young people of all countries have chosen the garbage disposal unit.
    Ivan Chtcheglov (b. 1934)

    Like bright metal on a sullen ground,
    My reformation, glitt’ring o’er my fault,
    Shall show more goodly and attract more eyes
    Than that which hath no foil to set it off.
    William Shakespeare (1564–1616)