Remember the word FOIL. F for FIRSTS, O for OUTERS, I for INNERS,
and L for LASTS.
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The FIRSTS are the 7y² and the y²
(7y²+x)(y²-2x)
That's because the 7y² comes FIRST in the (7y²+x)
and the y² comes FIRST in the (y²-2x)
So we multiply them together
7y²·y² = 7y4
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The OUTERS are the 7y² and the -2x
(7y²+x)(y²-2x)
That's because the 7y² and the -2x are on the OUTSIDE
(That is they are the farthest OUT from each other)
So we multiply them together
7y²·-2x = -14xy²
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The INNERS are the +x and the y²
(7z²+x)(y²-2x)
That's because the +x and the y² are on the INSIDE
(That is they are in the middle)
So we multiply them together
+x·y² = +xy²
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The LASTS are the +x and the -2x
(7y²+x)(y²-2x)
That's because the +x comes LAST in the (7y²+x)
and the -2x comes LAST in the (y²-2x)
So we multiply them together
+x·-2x = -2x²
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Write down the four terms from above for FIRSTS, OUTERS, INNERS, and LASTS:
7y4-14xy²+xy²-2x²
The two middle terms are like terms, so they will combine as -13xy²
Answer: 7y4-13xy²-2x²
Edwin